I need to fill out a form because my boyfriend claimed me as a dependent so I need to fix my return please advise

If your return was rejected because you had already been claimed all you can do is print, ink sign and mail in the return.  

Are you actually your boyfriend's dependent? For him to legitimately claim you as a dependent, all of the following must be true.

• You do not meet the requirements to be a qualifying child of your parents or anyone else (whether or not your parents actually claim you as a dependent).
• You lived with your boyfriend for the entire year - all 366 days.
• Your gross income for the year (2020) was less than $4,300. Unemployment benefits are included in gross income.
• Your boyfriend provided more than half of your total support for the year.
• You are a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.
• You are not filing a joint return with your spouse, if you were married to someone else at the end of 2020.

What exactly is the status of your tax return? Did you already file it, or did you try to file it and it was rejected?

(Note to anyone else reading this - This is not a complete description of the requirements for claiming someone as a dependent. It is specific to the situation described in the question.)