The method of heating a sandwich with a steamer is as follows:

1. Prepare the sandwich: Choose your favorite sandwich ingredients, such as bread slices, ham, cheese, vegetables, etc.

2. Heat the steamer: add enough water to the steamer and bring the water to a boil.

3. Use a steaming net or steaming tray: Place the steaming net or steaming tray in the steamer, ensuring there is sufficient distance from the water surface.

4. Place the sandwich: Place the prepared sandwich on the steaming net or steaming tray.

5. Cover the pot: Cover the steamer with a lid and make sure the lid is sealed.

6. Steam the sandwich: Place the sandwich in a steamer and steam over medium heat for a few minutes. The specific time depends on the desired degree of heating and the thickness and ingredients of the sandwich.