Hi @betaji
Ordinary enamel paint is no good to use as it gets very hot inside a microwave oven.
Make sure that you remove any paint that is starting to peel and then sand back the edges between the painted and unpainted areas smooth and then paint over with a [https://www.google.com/search?client=firefox-b-d&q=microwave+cavity+paint|microwave cavity paint] (examples only).
Here's just one [https://www.youtube.com/watch?v=z9RYay7EI80|video] that may help with painting the oven.