Trying to create a login page (unsuccessfully)

I am creating a clicker game for a school project. For saving data such as the players total currency or their upgrades, I figured that I would use google spreadsheets so players would just have a simple page where they login to their existing username (with no password, just the username) and continue where they left off or they create a new account. I’ve got the sign up working where it makes a new user, the problem I’m having is I don’t know how to create the login stuff (ex. checking spreadsheet for inputted username and then loading up that players game with all of their previous stuff. also, I would appreciate it if someone helped me figure out an autosave type system that would save the users stuff to the spreadsheet every 10ish seconds. thanks for your time.
p.s. if you have any tips regarding other issues/problems or just general improvements, please let me know

Link to app: Thunkable

When the user signs in, you would need to search the data source to see if that username exists. If you don’t have passwords then someone else can use the same username as anyone else. If the username exists Update the data in that row (or just get values from it as needed). If the username does not exist, Create [a] row and add the user’s data to it.

By the way, it’s best to avoid putting blocks that need special timing outside of the “then do” section. In this set of blocks, the second navigate block will probably fire before the create row block completes. I would delete the second navigate block.