I have not yet filed my 2016 return (status printed) but want to add some more deductions. how do I do it?

Yes.  How to finish a prior year online return https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb... 

If you paid for the online version, you need to call in and ask for the Desktop program.