What you have is known as either a 'popsickle' or a 'whole cook'.
A popsickle will be in a bag with brine...hence popsickle...a whole cook will be in a net with some glaze.
Both are fully cooked......just slack out under refrigeration for 6 hrs whole cook and until the brine is complete liquid for a popsickle (24 hrs).
You can bake, broil, grill or steam, but remember, you're only reheating...not cooking.
You want an internal temp of at least 165 degrees....but maybe be safer to bring up to 180 or so.