I'm testing my MAS app using Sandbox Test accounts - when I start the app I get the sign-in dialogue with the Apple ID field filled in with a previous account, and ready for password entry. However I want to change the Apple ID to use a different account but it won't open that field to edit.
I'm sure this has been possible in the past - but now it is just frustrating - there doesn't seem to be a way to escape out of the pre-populated Apple ID.
Further update - this seems to be a Mojave "Feature" as the abiilty to change Test Accounts is still available in High Sierra.
We have the same issue. There should be some easy way to switch between different sandbox Apple ID accounts. iOS has this feature, but mac doesn't, which is great dissapointment…
delete old tester ID (appStoreConnect -> User -> Testers)
Clean Build Folder
Rebuild and run the app