Once you file nothing can be
changed. First you will need to wait and see if your return is Accepted or Rejected by the
IRS.If the return is Rejected you can
go back in and fix the mistake without amending. If the return is Accepted you
will need to WAIT
until you receive your refund and then Amend to add your dependent.
Follow these steps to amend:
https://ttlc.intuit.com/replies/3288565
