At some points, we find inside of our enamel mugs get stained and cooking pots can get a lot worse. You don't need hours of scrubbing to remove them. All you need is baking soda and water.
Sprinkle a bit of baking soda onto the stained enamel, add a little of water and detergent to make it paste-like and scrub it. Light stain will go away easily with this way.
In extreme cases, put the boiling water with baking soda and detergent, leave it a while and scrub.
** Do not scrub with steel, it will damage the enamel coat. If food is stuck on the surface, scrub with a wooden spoon.