What form do you mail in with an amended 1120S?

[Plarka]

Is there a form to mail in with the amended return?

[MindyB]

There is no separate form like a 1040-X for a corrected 1120-S, you will send the 1120-S, and indicate it is amended. 

The corrected Form 1120-S should be completed in its entirety with the Amended Return checkbox selected. See: Amended and superseding corporate returns.