The best way way to clean oven that has been ignored far to long!

Vinegar and baking soda! Check out this link.

https://www.thekitchn.com/how-to-clean-an-oven-cleaning-lessons-from-the-kitchn-201191

The best non-chemical way is to use baking soda and vinegar. I would suggest, first trying to vacuum anything that is dried, if you can. Then mix the baking soda with water to make a paste and smooth it all over the inside of the oven. Get a spray bottle and mix plain white vinegar with water 50/50 then spray it all over the baking soda. Let the whole thing sit for an hour or so to give it time to work. It should pretty much liquefy all of the stuff on there so that you can wipe it clean with clear water. If any spots remain, do them again. Most of the time, they will come off. Wishing you the best.

https://www.hometalk.com/categories/cleaning/appliances/ovens

Don't be afraid to use your self cleaning setting, it works great, just remove the oven racks before setting it to clean. After the cycle is done, just take a damp sponge and wipe out the white coating it leaves from cleaning and you may need to take the vacuum to suck out any small particles. It will look great and you will be all done. I love the self cleaning feature.

Pennie's right - self cleaning is great - no chemicals involved!

I agree with Penny, just make sure you can ventilate the house for a while. It really smells but does a great job.