Did you already file it?  If you filed you have to wait to see if it is Accepted or Rejected,  If you haven't filed yet or it rejects you can fix it and resend it.  

If you filed and it gets Accepted do NOT change it yet.  You have to wait for it to fully process and you get the first refund.  Then you can mail in an Amended return to fix it.  The amended return won't be ready until late February.  If your return does get accepted before your father's return then he will have to mail his return this year.

When you have your return open on the screen there is a Personal Info tab.  Click Edit by your name and scroll down to #3.