To avoid needing to complete Schedule AI of Form 2210 (if doing so would be required to avoid a quarterly underpayment for earlier quarters), you could consider manufacturing tax withholding which would apply to earlier quarters by, before the end of 2023, having your husband obtain distributions totaling more than the RMD so that enough can be withheld to cover the entire tax liability, then using other funds to complete the rollover of the amount distributed in excess of the RMD. If the RMD is from an IRA, rolling the funds back into a traditional IRA would be subject to the one-rollover-per-12-months limitation.
