At this time, you can only link one bank to EarnIn. This is referred to as your linked bank account. This must be your primary account where your direct deposit is sent.
If you want to change your linked bank account, you can do so any time in the app settings. More info: How to change your linked bank account
Some EarnIn products involve opening a deposit account with one of EarnIn’s partner banks. This is in addition to your linked bank account.