After you file

You say that your brother "wants" to claim you --- but you have provided no information as to whether your brother paid for over half your support, how old you are, whether you are a full-time student, etc.etc.   We have almost no information to go on.   

What we can tell you is that if you have already filed, and the IRS accepted your return that says you cannot be claimed, then anyone else who tries to e-file a return with your SSN on it will be rejected.   If your brother CAN claim you as a dependent, then the only way he can file now is by mail.  He will have to print, sign and date his return and mail it in.  Even if you amend, he will not be able to e-file with your SSN on his return this year----the ONLY way he can claim you is to file by mail.

If you made a mistake when you said you cannot be claimed then you can amend.   You will have to change the way you answered the question in My Info that asked if someone else can claim you.  Your amended return ---even if you amend soon----will not enable your brother to e-file.  He can mail his return whenever he is ready to mail it.

As for whether your brother can claim you----here is the criteria for him to use:

IRS interview to help determine who can be claimed:

https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent

WHO CAN I CLAIM AS A DEPENDENT?

You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2023 taxes as long as they meet the following requirements:

Qualifying child

• They're related to you.
• They aren't claimed as a dependent by someone else.
• They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They're under the age of 19 (or 24 for full-time students).
• No age limit for permanently and totally disabled children.
• They lived with you for more than half the year (exceptions apply).
• They didn't provide more than half of their own support for the year.

Qualifying relative

• They don't have to be related to you (despite the name).
• They aren't claimed as a dependent by someone else.
• They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They lived with you the entire year (exceptions apply).
• They made less than $4,700 in 2023.
• You provided more than half of their financial support.

If you need to amend:

See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...