How to Reheat Pork Tenderloin:

Choose pan that will fit the meat in a single layer and have a lid for that pan. Add a very thin film of oil to the pan and
heat over medium heat until the oil is shimmering. Add sauce.
I prefer a gentle, rather than high, heat to minimize the risk of overcooking. Add the pork tenderloin to the pan in a single layer and immediately cover with the lid. Flipped every minute or so and it take about three minutes total.