S corps file their returns using Form 1120S. An S corporation generally has three years to amend its return. To do so, it files an updated Form 1120S and checks the box on Line H for "Amended Return." ...

How to Amend a Corporation's Tax Return. You may want to amend your corporate tax return if you forgot to ... Since Form 1120X doesn't includes all the steps found on the original Form 1120, ...

Know how to file an amended return. ... Corporations and S corporations will use Form 1120X and Form 1120S, respectively. Form 1065X is for partnerships and multiple-member LLCs.