Originally Posted by
ISTFlyer
TK won’t rebook you to another carrier but provide you a hotel in Istanbul. If you need to access your destination earlier than the alternative that TK provides, before confirming the changes, ask to cancel your booking without any penalty and then book yourself on another airline.
The OP is on an award ticket which makes this far more complicated (in particular if this is not a TK M&S award). Accepting a refund and rebooking on his/her own will most likely not work for the OP in this situation.