Where asked to enter the spouse's Social Security number enter 999-88-9999. You can only print and mail the tax return, it cannot be e-filed. When you print the tax return erase the Social Security number for the spouse and manually enter NRA for non-resident alien.
See this TurboTax support FAQ for the procedure to print and mail a tax return using the online editions - https://ttlc.intuit.com/questions/1944348-how-do-i-print-and-mail-my-return-in-turbotax-online
