My return was rejected due to a dependent being claimed elsewhere. I can't tell which dependent or who attempted to claim him or her. How do I fix this?

You will have to print and mail your tax return including all of your dependents.  Any refund on your tax return will be paid. 

The IRS will contact you and the other party by mail within a year to start an investigation on who can claim the dependent.  The loser of the investigation has to pay back any refund based on the dependent plus penalties and interest.

See this TurboTax support FAQ for printing a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/printers-printing/print-mail-return-turbotax-online/L5bwuqXGy_US_en_US?uid=m9bbfbxc