The window and passcode are optional parts of the game, but I can also explain what to do with them if you need to.
And so, if you have found the Messiah, then you are already in the maze. Keep wandering around until you find a house. There will be a mother there and you need to interact with her(if you have already picked up a syringe earlier). There you will receive the item necessary for further advancement.
Also, regarding the passcode. Before activating it, take the coin in the black and white location with cockroaches. If you already have it, go to the locker in the red area and enter 1995 there. There, find Gaspar and the vending machine next to him. Interact with the machine with a coin and you will receive the key to the window. There will only be a cutscene, but if you plan to explore all the content in the game, why not?