how do i record tape input as it's own track on studiolive 16.4.2 AI?

If you open the Aux Inputs router in UC Surface, you can assign the Tape Input to one of the 16 auxiliary FireWire sends. Once assigned, use this as the input to your DAW application. (i.e. if you assign the Tape Inputs to Auxiliary Sends 17-18, you would select 17-18 as the input source in your DAW)