If the 2019 Form 8889 is wrong, amending it would require filing Form 1040-X and the corrected 2019 Form 8889. If the underreported amount is of a personal HSA contribution filing the amendment would likely result in a tax refund. You should at least prepare the corrected Form 8889 to see if it results in a tax refund or if it shows an excess contribution before deciding whether or not to file the amendment. I'm not going to offer an opinion on whether you should file the amendment or not.
The opinion that I will offer is that a CPA should not have made this mistake.
