From 2020-51:

"D. Permitted repayments of RMDs previously distributed from an IRA. In the case of an IRA owner or beneficiary who has already received a distribution of an amount that would have been an RMD in 2020 but for section 2203 of the CARES Act or section 114 of the SECURE Act, the recipient may repay the distribution to the distributing IRA, even if the repayment is made more than 60 days after the distribution, provided the repayment is made no later than August 31, 2020. The repayment will be treated as a rollover for purposes of § 408(d)(3) of the Code, but will not be treated as a rollover for purposes of the one rollover per 12-month period limitation in § 408(d)(3)(B) and the restriction on rollovers for nonspousal beneficiaries in § 408(d)(3)(C)."