Step 1: Launch the Game.

Step 2: Navigate to the "OPTIONS" menu at the top of the game window.

Step 3: Click the "CONTROLS" option.

Step 4: Under "Player Controls" choose one of the "Joystick" options in the number 1 category provided and that should connect your controller! If you get an error on all 4 then that means your controller isn't connected properly.

If these steps are followed correctly then you should be good to go!

(Disclaimer that it may show what looks like 4 players can connect to the game but I will say this now that Derealized is NOT a multiplayer game and that is just a default option clickteam games give even if the game itself doesn't offer it.)