You're on the account you want to transfer/play on.
From the main lobby, select the menu icon in the top right corner.
Select Data Transfer and Transfer Settings then select your method; for example Sign in with Google and Link your account.
On the new device you want to play your Exedra account on, open up the Magia Exedra App.
DO NOT GO PAST THE TITLE SCREEN TO THE MAIN LOBBY; STAY ON THE TITLE SCREEN.
In the top right corner there's a button that says Support, select it then Data Transfer.
Finish up with your method of transfer you started; for example Sign in with Google and it'll give you the option to Link your account and possibly delete the account that is on the device you're currently on (should be a new default account or one you're parting with).


Why did I have a hard time?
I kept going to the menu screen from the main lobby and selecting Data Transfer from there. I believe you can only set up the account outgoing from there and not incoming. So basically start Data Transfer from Menu screen and end with the other Data Transfer button in Support on the title screen.
Idk maybe I'm immensely stupid and didn't need to write this. I couldn't find good information or a guide online. Don't ask me questions or bother me I'm just throwing this info out in case it saves someone else.