Scrub with baking soda or use a food safe degreaser like GP66.
Soak vinegar and baking soda overnight, then scrub!
You could try this: https://www.hometalk.com/29142677/how-to-clean-your-oven-with-just-baking-soda
Soak a small rag (about size of washcloth) in Amonia and place it on a rack. Close the door and keep closed overnight. In morning, the grease should just wipe out with a cloth. You may need to use a little scrubbie and scrub it out - It should just take a very gentle scrubbing. If your oven is gas, you MUST kill the pilot light so no gas gets into the oven.