If your return has been transmitted and rejected by the IRS, you can correct your tax return and re-transmit.
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.
If your return has been transmitted and accepted by the IRS, you will not be able to electronically file a second tax return with another service.
Amended tax returns will not be available before February 13. 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.
See also this TurboTax Help.
In the amended tax return, go to My Info. Select the box next to Another taxpayer can claim me as a dependent on their tax return.
You cannot amend yet---not until the return has been fully processed and not until the Form 1040X you need is available in mid-February.
Sadly, this means the only way your mom can file her tax return that claims you is by mail. She will not be able to e-file this year at all even if you amend. So she can mail her return whenever she has it ready for the mailbox.
Your part in fixing this is to wait until your return has been fully processed and you have received your refund. THEN you need to file an amended return, called a 1040X, to change the way you answered that question in My Info
If it is any comfort, you (and your parents) are among many young tax filers who make this mistake. We will be seeing plenty of posts just like yours. And posts from the parents whose e-files were rejected....
Wait until your original return has been fully processed before you amend, and make sure you have saved a pdf of the original return before you 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...
Do not expect quick results from amending. It can take four months or more for the IRS to process an amended return.
You can watch for information here:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1