Don't do what I did.
Don't phone LM. 40 mins on the phone and the agent and their colleagues couldn't find the TK PNR.
Instead, just log in to checkmytrip.com. Input AV PNR. It brings up full details, including TK PNR.
Don't try looking it up on Turkish web site. It's as useless as LM agents and won't allow the booking to even be viewed. (You can use it to create a dummy booking to see the seat maps though.)
This reservation cannot be viewed due to the sales channel in which it was formed.
You can apply to the channel where you have made your reservation to make a transaction.
Instead, just phone Turkish and ask them for the seats you want. (Under one tenth the time of my worthless LM call.)