I accidentally files my son (16 years old) tax return without declare he as my dependent. This is made my tax return was reject when I did e-files.

You have to file your own return that claims your son by mail.   Even if you amend his return, you will be blocked from e-filing your own return for this tax year since you used his SSN on a return that did not say he could be claimed.  Sorry.   Print, sign and date your return in ink, and mail it in.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as certified mail so you will know the IRS/state received the return.

Federal and state returns must be in separate envelopes and they are mailed to different addresses.  Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.

When your son's return has been fully processed it can be amended.  Amending his return will not allow you to e-file.

You will not be able to e-file your 2024 federal tax return as his Social Security number has been accepted on another tax return.  Amending his return will not change the IRS database for receiving tax returns.

You can print and mail your 2024 tax return now with your son added as a dependent.   The IRS will pay you the tax refund on your return, if any.

Amend your son's return ASAP to change him as a dependent on his return.