You can't transfer miles from one airline programme to another.

If you can book a reward ticket on TK via Lifemiles, then just go ahead and do that.

Unless you made a cash booking in Economy, you should be able to cancel that Economy reward for a refund. (less a cancellation fee)

It's not a good idea to have two confirmed reservations in your name on the same flight. At some point one might be automatically cancelled, and it might not be the one you want cancelled!