If the IRS accepts your return, then you have to
wait until it has been fully processed and you have received your
refund. THEN you can prepare an amended tax return 1040X and mail it
in. You cannot e-file an amended return. Meanwhile, DO NOT change
anything on your return until you start the amended return.
The 1040X form for 2018 hasn't been approved yet
by IRS. Please, keep checking the following information on how to amend your
return; it will be updated once the 2018 form is released:
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
