Amend prior year filing for successor sponsor

The situation has come up before.  5500-SF filed for a sole prop 401K with employees for 2021, extension 10/15.  Not knowing at that time, client incorporated in 2021 .  5500 for 2021 filed under sole prop EIN.

Form 5558 filed for successor for 2022.  Attempting to correct ASAP in order to avoid any IRS love letters, we could amend 2021 under new corp EIN and complete box 4 with info from predecessor plan and move forward to 2022, BUT won’t DOL/IRS look for an extension on the successor sponsor with successor EIN, which had not been file as we were not advised of the error previously??