They will have to mail in their return this year. this really can't be corrected by you filing an amended return.
you need to go back into your return and select amend. under the personal worksheet section
there is a question that asks, "can another taxpayer claim you as a dependent". check yes and also the next questions which asks is you were actually claimed. then review the other questions to make sure they are answered correctly. Perhaps you did and you no longer qualify to be claimed by them as a dependent. if you can ne claimed once completed you should be able to e-file your amended return.
these are the test for then being able to claim you as a dependent
You could be claimed as a qualifying child if all these tests are met
- You have the same principal abode as the other party for more than ½ the tax year. Temporary absences like for school are ignored
- If not a full-time student you’re under 19 at the end of the tax year. If a full-time student under 24 at end of tax year.
- you haven't provided over ½ your own support
- you didn't file a joint return unless there was no tax liability but merely filing joint to facilitate refund of taxes withheld or estimates paid
Or as you could be a qualifying relative if all these tests are met
You’re related to the other person or, if not, lived with the other party for the entire year and
- your gross income for 2023 less than $4,700 and
- the other party provided over ½ your support
