Customer refund / leftover 2019 vendor credit -- how to enter on Schedule C?

Working on Schedule C "Returns and Allowances" -- customer returned some equipment, which we refunded in full.  Manufacturer gave us credit instead of a refund for our cost.  It's 2020, and we still haven't used up the credit.

 

How do we document all of this on Schedule C?

 

Thank you!

Dede O'Hair