Hi @rachel5,
Welcome to the Community. I can help you with applying a check payment to an invoice.
It's always a good feeling when you see a customer payment. You can record the check payment with the following steps:
- Click the Plus sign and select Receive Payment.
- Choose the name of the customer, date of payment, and Check for the payment method.
- Enter the amount of the payment and select the invoice to apply the payment to.
- Click Save.
I'm including a brief video to serve as a visual guide:

For additional information on this process, such as how to use Undeposited Funds, I recommend the following articles:
That should take care of it. I believe that you'll have the check payment applied to the invoice in just a few clicks.
Please don't hesitate to let me know if I can be of further assistance. Wishing you well.