Look at each of the W2-s and see what year each it is for. For each year you would amend the tax return for that year. You would add the W2 amount for the amended year(s). You would want to file an amended return since there was tax withholding. You would also need to file an amended state return for those years that the W2s are for, ie for each year an amended federal return was filed you would need to amend the state return for each of those years. Hope this helps.
