OnePlus
Change Google Backup Account auf OnePlus
OnePlus phones let you link more than one Google Account at the same time. When that happens, the phone still only backs up your data to one account at a time, and it is not always the one you expect.
The account used for Backup is controlled separately from the account you use for the Play Store or Gmail. If your contacts, call history, or app data suddenly seem missing after a reset, chances are your backups were stored under a different Google Account than the one you are currently checking.
To switch the backup account on OnePlus, go to Open the Settings ➔ Tap on System ➔ Tap on Backup ➔ Tap on Account ➔ Choose a backup account. Pick the Google Account you want new backups to be saved to.
This setting only changes where future backups go. It does not move or merge data that was already backed up to another account.
If you plan to sell the device or hand it to someone else, changing the backup account is not the same as removing your data. For that, remove the Google Account entirely or reset the phone.