My first idea would be to try using a Stored Variable for this. Assign the UserID to a stored variable when the UserID gets created. Then, when they press the exit button, you can use the UserID text to find the corresponding row number in the Google Sheet. Once you know the row ID, it should be simple to use the update value block to update the columns.
Because it’s a Stored Variable, the UserID should be saved in between user sessions on the app.
Someone posted a method to find the row number based on the contents of a known column recently, check out: How to get data for an individual user from a google sheet? - #4 by jakecohen120rpcjvw - the latest reply has a Youtube tutorial
Mind you, this only works if the UserID is a unique value. I’m not sure how your app would be used exactly, but a random number between 1 and 100 can run into issues. Perhaps you could use the ‘Seconds since 1970’ block to assing a UserID instead? This block is in the Device category.