The quest can be taken at the Bazaar, from Damien after meeting Carl and Sophie in the plot of Dying Light 2. Follow the marker, enter the building and chat with the guard. After going down through the hole, talk to the Investigator. If you ask what kind of work, the Investigator and his friends will attack you. Defeat all the enemies and try to get outside to face Damien. He will talk about his brother. Choose how to proceed. We decided to help Damien save his brother. Or you can turn Damien in to Carl.
Follow the marker to the indicated building. Climb to the roof and find the entrance - a broken window. Search the shelves inside the building. There is cassette. Find a hole in the floor and jump down. Move down the stairs, past the zombies, until you find yourself on the first floor, where the bandits are. Defeat all enemies and go through the door. Talk to Cliff. Kill the normal enemies and then deal with Cliff, Damien's brother. After getting outside, run along the marker back to the Bazaar. Talk to Roger, who will say that Damien has locked himself in the tower.
Exit the church through the main entrance and look to the left. Start climbing up the tower by moving along the boards and jumping over the rungs. Inside the tower, cling to the metal beams on the walls. Climb to the roof and enter the indicated tower. Look up at the ceiling to see an opening with yellow planks and jump up. A poster with a skull hangs in a small room, and a note "Secure Code" (memorabilia) is hidden behind it. It contains the password for the safe nearby - 510. Inside the safe, you will find "Carl's Diary No. 4" (cassettes). Climb even higher using the hatch under the ceiling. This is how you meet Damien. No need to talk about his brother or Damien will jump down. The right option is to talk about life. After that, the task will end.