To avoid confusion, it is usually best to wait and amend a return after the IRS has accepted the original return and you have received your refund, if applicable.
If this is a new return (i.e. you did not originally file through TaxAct from this account), first enter the information so the return mirrors what is shown on your originally filed, printed copy and then follow the steps below to complete the amended return.
If you receive an error when accessing Amend Federal Return that states you must first complete the Filing steps prior to Amending the return, click Filing (on smaller devices, click in the upper left-hand corner, then select Filing), then click Mail Paper Return. You will just need to proceed through these screens until you are prompted to actually print the return. (You will not need to print the return, just clicking to view it is sufficient.) Once you do this, you can go back to the Filing section and choose to amend the return to complete the process.
The IRS supports both paper-filing and e-filing for amended 1120 returns. At the end of the Amended Federal Return section, you will be prompted to choose either Paper Filing or Electronic Filing.