Preheat the oven to 300°F to 350°F
Wrap the croissant loosely in foil if you want a softer result
Place the croissant on a baking sheet
Heat for 5 to 10 minutes
Remove the foil for the last 1 to 2 minutes if you want a crispier exterior
Let it cool for 1 minute before eating
Use a toaster oven at low heat for a small batch
Microwave for 10 to 15 seconds only if you need a very quick reheat
Avoid overheating to prevent drying out the croissant