Hi amy-tower,
Welcome to the QuickBooks Community. The program allows you streamline your work using the powerful features offered in the program. Rest assured, I'll be happy to share more info so you're on the right track.
Currently, QuickBooks Online doesn't have a Company Setting to set a default bank account such as the one you've described. However, the program uses "sticky" settings. It will remember the bank account used in the last transaction of that type. I can see the benefit of having the function you've described and I encourage you to send feedback about this to our engineers. You can send feedback by clicking on the Gear icon and looking for Feedback.
Let me know if you have other questions by leaving a comment below. I'll be one message away.
