What is the reject code? The 2 digits after the 3 digit code might indicate which dependent. Here’s a couple reject codes that may help
Reject 507 duplicate ssn
https://ttlc.intuit.com/turbotax-support/en-us/help-article/taxation/fix-e-file-reject-ind-507/L67xx...
Reject code 517
https://ttlc.intuit.com/turbotax-support/en-us/help-article/rejected-tax-return/fix-e-file-reject-in...
If it thinks another return has been been filed then you have to print and mail your return and let the IRS sort it out.
If a ssn on your return has been used on another return it could be just a mistake and someone else accidentally typed the wrong ssn on their return. Or if your dependent filed a return did he check the box that says he can be claimed on someone else's return?
How to mail a return from the Online version
https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...
