If you claimed yourself on your tax return and you should not have, you can change it be going back to My Information and going through the interview to say someone else could claim you and is claiming you.
If you already filed your return, you will have to do this as an amendment and file an amended return on paper in the mail. It takes the IRS up to 16 weeks to process an amended return, so whoever is trying to claim you will not be able to e-file this year . They need to go ahead and claim you but file their return on paper in the mail.
How to amend:
https://ttlc.intuit.com/replies/3288565
