The non filer portal was only to be used by those not filing a tax return. When you used it, a tax return was efiled for you with 0 income. Now you must print and mail a return to get it accepted.
You would normally have to prepare, print and mail an amended return form 1040X in this situation. However, many of us believe that you can bypass the 1040X by preparing your "real" original return, printing it, and writing "Amended Return" on the top of the 1040 form before mailing it. Use the filing instructions that will print with the return to see what to include and where to mail it.