How do I transfer global variables from one layout to another?

Are you using the same event sheet for both layouts?

If not, go to the second event sheet → right-click → Include Event Sheet. This allows the second one to read/write to the variables of the first one.

If you don't like this approach, you can also create an event sheet just to store these kinds of variables and include it wherever you need.

I'm trying to make a global variable that stays the same when the user enters another layout. Is there any way I can do that?

You don't have to do anything - global variables always retain their value when you switch between layouts. Unless you reset them with "Reset global variables" action.