Do you mean the RMD rollover that had to be done by August 31st, 2020?

https://www.irs.gov/newsroom/irs-announces-rollover-relief-for-required-minimum-distributions-from-r...

It might be possible to recharacterize the RMD as covid disaster distribution, if it qualifies. Read the Form 8915-E instructions to see if your clients' situation meets those requirements. If so, repayments are possible as the "rollover" period is three years in this case. Also read the section that describes how to report repayment, in case that requires 1040X for 2020.