While the IRS Closing a Business video mentions marking a Schedule C (Form 1040) Profit or Loss From Business as a "Final Return" in the space at the top of the last Schedule C filed for a business, they do not require this or actually use it in any way. It would only be for the benefit of the tax filer to mark it with those words, and that can be done on their paper copy of the final return.
The forms in the TaxAct® program, which includes the Schedule C, go through a series of testing with the IRS to be approved before usage each year, so the form in the program is the form that is approved by the IRS. If you insist on marking the return as a final return, the only option is to mail in a paper copy of the return and manually write "Final Return" at the top of the form. You can also contact the IRS to see what their guidelines are regarding this issue. The toll free number for the IRS is 1-800-829-1040.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.