After you file

If you did not use direct debit, it will not be withdrawn.

 

Otherwise, amount already paid or expected to be paid goes on 1040-X line 16.

 

I recommend stating up front in Explanation:

"This is amendment No.2 correcting <xyz> error on 1040-X No.1 already e-filed."

 

You don't have to wait.

 

@vreale1