First make a paste with 1 cup baking soda and 1/3 cup water. Spread the paste on the oven areas that need cleaning or all over. Let it set all night. The next day spray or spritz the white vinegar on the baking soda. It will bubble up. Wait ten minutes or so and wipe clean with a damp sponge or rag. Repeat the paste and vinegar treatment as needed. I do not let it set all night if I have to repeat the process. This will get it clean eventually. Keep up with the oven using the paste and vinegar as you use it to prevent long arduous cleaning steps.
Maybe this will help