its simple create a game instance bp and change game instance setting in project settings to the new blueprint that you made then make the variable inside of the game instance bp that you created and then whereever you want to use the variable cast to the instance blueprint that you created then connect in to the oblect the get game instance then access whatever variable you stored there you can also do that with gamemode and the game mode is for variables to be stored for levels and be accesible only on certain levels and the game instance is for variables that are used througout the whole game and are used in multiple levels i hope i helped
here’s a video tutorial showing how it works:
in the photograph i access a variable inside of game istance blueprint.