Assuming it was fully cooked
I think all you will ant to do is heat it enough to get the interior warmed up.
Check it with a thermometer and if it's up to 130-140 ish, I think you can take it out of the oven.
Do you not have a kitchen scale? I could not live without mine.
(I also use the scale to weigh packages I am shipping, so I can buy postage online and save money)