I wouldn't worry about it. In my experience they never apply it anyway.

Just mail the voided paper refund check back with a 2021 1040-V voucher. 

My notes from the last time I had this situation say "Write "VOID" across front and back of check. Write on the face of check Apply to - Name, SS#, Form#, YR: and mail to the Service Center they paper file returns with. Make a copy. Mail by certified mail."

Not acceptable answers. Was able to get ahold of tech support and fix the issue.