Happy to see you back, @lxsgreen.

You can apply it to another customer by unlinking the payment. Once done, change the name of the customer. Then, link the Invoice to the correct one.

Base on the screenshot you've shared, click the Yes button. Once done, apply the payment to the correct customer.

I've added this article to know more about the process: Record invoice payments in QuickBooks Online.

 You may consider checking this reference for your future task when you're ready to assess your business financials: Reconcile an account in QuickBooks Online.

I'll be here if you have other questions. Don't hesitate to let me know in the comment section. Have a good one.