If your tax returns for those tax years have already been filed and accepted by the IRS, then you can only amend the tax returns. You cannot just re-file as originals.
Each tax year would require you to complete an IRS Form 1040X, Amended U.S. Individual Income Tax Return. A federal amended tax return, Form 1040X, can only be printed and mailed, it cannot be e-filed.
Additionally, since you paid the CPA for completing those tax years, then the CPA should file an amended tax returns for you.
