Welcome to the Community, @suecarletta.
I'm here to help you correct a Project for a Customer in QuickBooks Online.
At this time, once a Project is assigned to a Customer, you can no longer change it. As a workaround, you'll need to delete the Project and assign it to the right Customer. You can refer to these Community Articles to make changes in your account:
if you have any additional questions or concerns, please don't hesitate and reach back out to me! I'm always here to help you in any way that I can. Have a good one.