All you need is a dishwasher tablet! The oven will be like new again

Make sure the oven is turned off and cooled down before you begin cleaning.
Dissolve dishwasher tablet: Fill a small bowl or cup with warm water. Put the dishwasher tablet in and let it dissolve by stirring it gently. You will get a kind of paste.
Apply the paste: Dip a sponge or soft brush into the resulting paste. Apply the paste generously to the dirty areas of the oven. Pay particular attention to the areas that are most contaminated.
Leave on: Leave the paste on for about 15-20 minutes.