Find Stamp, The Nose Knows, Check the Route, and Train Yard Security are quests in Chapter 5, "Mad Dash", in Final Fantasy VII Remake that take place in Corkscrew Tunnel. Cloud Strife, Barret Wallace, and Tifa Lockhart travel through the Corkscrew Tunnel to find Mako Reactor 5. The group navigates by following graffiti of Shinra propaganda mascot Stamp.
Walkthrough[]
From where the quest begins, follow the track as it bends right. On the way, a door leads right to a small corridor, at the end of which is a room with a treasure chest containing an elixir. Slug-Rays appear along the path, which should be staggered before defeating them with abilities and spells. Continuing further down the track there are stairs on the left that lead to the end of the hall and to a group of wererats guarding Shinra boxes and a chest containing a star pendant, an accessory that makes the wearer immune to 
Poison.
Further down, Slug-Rays are encountered alongside elite grenadiers and guard dogs; as before, they are best dealt with by staggering them with attacks before unleashing abilities and spells. Another door to the right leads to a corridor, at the end of which is a treasure chest containing an ether.
Shortly after this, graffiti is found behind a set of stairs. Follow Barret and Tifa up the stairs, then head up after a brief dialogue where wererats are fought, which can be defeated quickly with regular attacks. Descend the stairs, grab the treasure chest, and then go down more stairs onto a walkway, where wererats and grashtrikes are fought; these are slightly tougher than wererats, but can be defeated with abilities and spells (especially 
Blizzard to exploit its weakness) after staggering. A few cobwebs block the way, which are cleared by interacting with them. Stairs lead down to the side of the tracks, where more grashtrikes appear, along with the queen grashtrike. This enemy is more durable, and can leap at characters to stun them. Dodge the leaping attacks, and use Blizzard, Barret's Overcharge, or Tifa's martial techniques imbued with Unbridled Strength to pressure it, then stagger it and lay into it with Cloud's Punisher Mode and Tifa's martial techniques.
Once the queen grashtrike is defeated, the party will need a way forward. Instead, head back and remove the cobweb blocking the way to another set of stairs. A treasure chest contains three phoenix downs, and graffiti is marked on the way up. Head up to a walkway and down, where security officers and a flametrooper are fought. The flametrooper is a durable enemy who can fire a flamethrower that deals considerable damage if not avoided. It is weak to 
Fire, and resists physical damage. It can be hit from the back to destroy its fuel tank, dealing significant damage. Aside from this, cast Fire against it and use Barret's Overcharge or Tifa's Unbridled Strength martial techniques to stagger it, while using the security officers to build up ATB gauges.
Once the flametrooper is defeated, head up along the construction material to the north end of this platform, then interact with a gate on the left to return to the tracks. Barret will run over to another platform; talk to him to commence a brief cutscene. After this, the path forward is to simply follow the track route left. On the route leading straight, a door on the righthand side leads to a hallway with a room at the end containing a leather bracer, though there is otherwise nothing of value, and Barret or Tifa will stop Cloud if he continues through this way. Along the route left, a few security officers are fought, but these are easy enemies.
After following the path left, Tifa will note that the way forward is blocked. Talk to Barret, who will say to defeat the enemies ahead. Here, two flametroopers and sentry launchers are found. This is a challenging battle, as the launcher's missiles can deal significant damage if not dodged, as can the flametrooper's attacks. Sentry launchers can also create a burst of electricity around them, though this will be telegraphed. However, as the launchers are stationary enemies, the flametroopers are a bigger threat. Attacking them in melee range is deadly, as it will mean a character is caught between the flamethrowers and missiles.
It is better to lure a flametrooper out, wait for them to use their attack, and allow another character to hit them from behind while also casting Fire against them. Hitting their fuel tanks with Tifa's martial attacks is also effective. Stay defensive and heal often, while making sure to pick off the flametroopers and avoid the sentry launchers. Once the flametroopers are destroyed, focus on the launchers. Thunder is effective against them, and Barret can attack them from range to avoid their attacks, while Cloud and Tifa need to frequently dodge out of their lightning bursts before running back into deal damage with Punisher Mode or Unbridled Strength attacks.
Once they are defeated, the quest continues in "Secret Passageway".
Hard mode tips[]
Against most enemies, the strategies are the same as before, with the addition of new character abilities that prove helpful, such as Cloud's Triple Slash allowing him to hit multiple enemies quickly, Tifa's Starshower allowing her to deal significant damage while being temporarily invulnerable, and Barret's Maximum Fury allowing him to deal a burst of damage. Against the queen grashtrike, casting Haste and Regen is useful not only to counteract its inflicted statuses, but to provide much-needed sustainability.
Against the flametroopers, equipping 
Fire Materia paired with 
Elemental Materia on armor can resist against, or even heal from, their attacks, making the battles considerably easier than before. A great way to destroy the sentry launchers and flametroopers is by using Tifa's Starshower followed by True Strike to deal considerable damage. Though lightning spells can be used as before, it is better to save MP for the boss fight that follows.