My taxes have been accepted. I have not received my refund. But I need to remove a dependent. I did not know that it was my son's mother's year to claim him.

[JamesG1]

If your return has been transmitted and accepted by the IRS, you will have to amend your Federal 1040 tax return.  However, before amending your tax return, do not enter the return and do not make any changes.

Amended tax returns will not be available before the middle of February.  See forms availability here.

If you used TurboTax Online, log in to your account and select Amend a return that was filed and accepted.

If you used the CD/download product, sign back into your return and select Amend a filed return.

To remove a dependent, click on My Info down the left side of the screen.  Then click the trashcan Delete icon to the right of the dependent that needs to be removed.

See also this TurboTax Help.

[xmasbaby0]

If you made a mistake and claimed a child when you should not have done so, alert the other parent asap.  When they try to e-file their return claiming the child, their e-file is going to be rejected.   They will have two choices----one would be to print, sign and mail their return that claims the child.   They do not have to wait for you to amend.  Waiting will not help them at all.

The other possibility for them is to get IP PIN's and try to e-file:

GET IP pin in order to e-file if your dependent’s SSN was claimed on another return

https://www.irs.gov/newsroom/irs-takes-steps-to-help-prevent-refund-delays-by-accepting-duplicate-de...

https://www.irs.gov/identity-theft-fraud-scams/get-an-identity-protection-pin

Whichever remedy the other parent chooses, they have no reason to wait for you to amend.   Your amended return will take months to be processed.   And...you can expect to pay back child-related credits that you receive for claiming the child.