Hello ayaroch,
We understand that you don't want to use the Undeposited Funds account for your mobile invoice payments. However, we currently don't have a setting in QuickBooks Online Mobile App to change the Deposit to fields to the desired bank account.
It'd be best sending us feedback about it by clicking on the Gear icon and selecting Feedback. For now, you'll need to log in the QuickBooks Online using a browser, and deposit the payments using the Bank Deposit function.
We'll be glad to help you if you need anything else.