Escape to the Surface is a quest in Chapter 10, "Rough Waters", in Final Fantasy VII Remake, taking place in the Sewer System. Cloud Strife, Aerith Gainsborough, and Tifa Lockhart fall in the sewers, and must return to the Sector 7 Slums to prevent the plate from falling.
Walkthrough[]
The quest begins when the player controls Cloud. Both Tifa and Aerith have fallen on the floor beside him, and the player can choose who to rescue first, affecting which scene will play in the "Resolve" quest later.
Before doing so, the player may choose to ready their equipment for the following boss battle against Abzu. Abzu is weak to 
Fire, meaning the player can equip Cloud or Tifa with the 
Fire Materia paired with the 
Elemental Materia to improve their damage (Tifa has a higher 
Attack Power stat, meaning she will benefit more, while Cloud is proficient both in physical attacks and casting fire spells). All characters should have the Healing Materia equipped, and their weapons should have all available SP spent. 
Ifrit Materia should also be equipped, and having Cleansing Materia on someone to cast 
Poisona is also helpful.
Abzu boss[]
Abzu.
Abzu will use mostly melee attacks, and can occasionally jump to latch onto the sides and pounce at a character, binding them; at this point, the player should switch to another character to apply attacks on them. Casting Fira can exploit its weakness to fire damage and pressure it, as can crippling its left and right horns. Its attacks can also inflict 
Poison.
The boss' stagger gauge does not increase much from magical spells, meaning Aerith is best focusing on healing, while Cloud attacks with character abilities, and Tifa uses her abilities as well as her martial techniques with Unbridled Strength. When it clings to the wall, casting Fira against one of its horns can pressure it and cause it to fall. When the boss uses Pounce, dodge against it and it will stumble, giving Cloud and Tifa an opportunity to inflict more powerful attacks against it. Focusing on its right or left horn with spells can also cripple and pressure it, meaning it can be staggered. Once it is staggered, Tifa's Unbridled Strength techniques should be used to increase the damage it receives.
After Abzu loses half its HP, it will become enraged and use more the more deadly Triple Strike attack, which must be avoided, as the attacks can be devastating even when guarded against. It can also use Blackwater Blast, causing the water pools to damage characters if they stand within them. Keep avoiding attacks and guarding at all times, and take advantage of moments when it is stationary to cast spells and use more powerful attacks. Keep at range from it when it charges its attacks, waiting until after it has finished an attack to move in.
After Abzu is defeated, a cutscene commences. Approach Tifa for some dialogue, commencing the next quest, "Follow the Waterway".
Hard mode tips[]
Aerith is best focused on spellcasting. Between Cloud and Tifa, whoever has elemental materia equipped should focus on physical damage, while the other joins Aerith in spellcasting in addition to physical damage. Therefore, one should have a weapon focused towards physical damage, while the other has a weapon either with balanced attributes or a magic focus. Tifa is faster between the two, though Cloud has a naturally higher MP pool.
For materia setups, elemental and fire materia should be equipped on Cloud or Tifa as with before, and for Aerith, MP Absorption Materia or HP Absorption Materia should be paired with fire materia so she can heal while casting spells against Abzu (she can also simply pair two fire materia with both HP and MP Absorption, to heal both at once). 
ATB Boost Materia and 
Refocus Materia are great on all characters, but particularly Aerith. Either Prayer Materia or a combination of healing materia with Magnify Materia should be equipped; the former will save MP and frees up magnify for another slot, while the latter allows Regen to be cast on all. Time Materia and Barrier Materia are also good options to equip, and it is possible to pair both with magnify as well as alternatives to pairing healing with magnify.
Aside from this, a variety of Complete Materia should be equipped, including Magic Up Materia and MP Up Materia on spellcasters, while the physical damaging character should use Luck Up Materia and Deadly Dodge Materia. Cloud and Tifa both benefit from Parry Materia, though Cloud slightly more so. Refocus Materia should be used on one character. Steadfast Block Materia is good on all characters, but particularly on Cloud.
Though this is only the first of many combat challenges throughout the chapter, it is acceptable to spend a lot of MP here, at least on Aerith who will have opportunities to regain it later using Soul Drain, while Cloud and Tifa can comfortably spend just over half their MP.
Aerith should use Arcane Ward as the battle begins for her and the other spellcaster (if she opens with ATB Boost, she can place an Arcane Ward and immediately cast a spell after), and it is preferable to cast Haste or Regen if possible. Depending on their role, Tifa or Cloud should either be spellcasting in Aerith's ward. Casting Firaga can pressure and deal heavy damage to Abzu, and can cripple a horn immediately, allowing the physical damager to act. In a physical damage role, Tifa should use Starshower and Deadly Dodge to deal damage while avoiding Abzu's attacks, while Cloud in a physical damage role should use Counterstance and remain in Punisher Mode while parrying to deal damage while reducing Abzu's damage.
When Abzu uses Charge or Triple Charge, it is ideal to switch to Cloud and keep him in Punisher Mode (regardless of if he is used for spells or physical damage primarily) and brace for impact, as he is best-suited to reduce damage and can also Counterstance to deal damage of his own. When Abzu prepares Blackwater Blast after clinging to the wall, he can hit the entire party will be hit by great damage. Casting Firaga can knock him down to prevent this, though if this is not possible, Pray or Cura on all must be used after. If possible, Manaward can also be cast on all beforehand to resist damage.
Sustained fire attacks and defensive or evasive measures should eventually bring Abzu down. Defeating Abzu rewards Tifa the Way of the Fist Vol. VII.