BEFORE you do anything, look at if it is reasonable that they may have QUALIFIED for that amount of ERC.  There has been WAY too much fraud with that credit, and the IRS has warned tax preparers of amending returns to "perpetuate" an incorrect credit.

https://www.irs.gov/pub/irs-utl/2023-02-professional-responsibility-and-the-employee-retention-credi...