You will have to print and mail your tax return leaving him as a dependent on your tax return.
He will have to amend his return to change his dependency.
See this TurboTax support FAQ for how to print and mail a tax return when using the online editions - https://ttlc.intuit.com/turbotax-support/en-us/help-article/printers-printing/print-mail-return-turb...
