After you file


@Bert0 wrote:

If they were filed as married joint and they needed to be single, they would need to be refiled or? The deadline passed.... so what next?


If you were not legally married on 12/31/23, then you were not allowed to file jointly.  It would be allowable (and in fact required) to amend to 2 single returns, although the IRS might have some questions for you.