He will have to amend his tax return to include he can be claimed as a dependent. Amending his return will still not allow you to e-file.
You will have to print and mail your tax return since the IRS has already received a tax return with his Social Security number and not a dependent.
See this TurboTax support FAQ for how to print a tax return when using the online editions - https://ttlc.intuit.com/turbotax-support/en-us/help-article/printers-printing/print-mail-return-turb...
