Do I need to turn in my old TA-50 and if so, how?

Your last unit should have collected it during out-processing, before moving to the IRR. I have seen retired Soldiers with active OCIE records - It says "open" until someone manually goes in there and creates a FLIPL or your TA50 is received by the warehouse and cleared off your record. Not until all property is accounted for is the digital OCIE record closed.
You can check with your last unit to see if your OCIE profile is still under their command - if so, they can pull the turn in worksheet and help you get your gear to warehouse.
If your account is in a "transit" status, you may have you work with the warehouse directly. POC for warehouse Dominguez, Jamie; [login to see] [login to see] ; Meghann Souza [login to see] [login to see]

I got out of the Reserves and into the IRR just after 9/11.
I was told to hang on to my TA-50, I may need it.
My IRR contract expired in 2003, I went to my old unit and no one knew anything about my TA-50 or what to do with it. By then everything had went from the woodland stuff to digital.
I was told to hang on to it, and contact my branch manager. Who???
So finally in 2014, when I sold my old house, I gave all that crap to my nephews to play with.
I wasn't dragging that stuff around anymore.

Better, somewhere is a hand receipt, and they will want to take it out of your final pay!