Basically, you cook up a batch of spaghetti (or linguini) noodles. Meanwhile reheat your turkey gravy, thinning it out a bit with some milk, and add some Parmesan cheese.
Dice leftover turkey and stir it into the gravy/sauce. When the noodles are done, drain them and stir the sauce into the spaghetti.
You want measurements? Can’t do it, and it doesn’t much matter, but if you have about twice as much turkey as you do parmesan cheese, and more gravy/sauce than you do turkey, that’s good. But it’s pretty forgiving no matter what you do.