I'll be more than happy to assist you with changing you sales receipt details, @chelsel-casdk12-.
Customizing the Sales receipt under Product/Service allows you to modify its details from sales to donation. I'd be glad to walk you through the process.
Go to Sales from the left menu, then click All sales.
Click the Filter button.
Select Sales Receipts from the Type drop-down.
Choose the Customer that you want to modify, click Edit.
Scroll down, look for Product/Service, and change your sales to donation.