Preheat the oven to 275°F to 300°F
Place the fish on a baking sheet
Add a little oil, butter, or a splash of water to keep it moist
Cover loosely with foil
Heat for 10 to 15 minutes, until warmed through
Reheat in a skillet over low heat for a few minutes per side
Use a microwave only if necessary
Microwave on low power in short intervals
Check that the fish reaches 145°F internally
Avoid overheating to prevent dryness
Reheat only once