Easiest (and most effective) way I’d recommend is take the racks out of the oven. Fill the bathtub (or, if you have one, a large enough sink) with very hot water. You’ll only need enough to cover the oven racks. Add about a 1/2 cup of dishwashing soap (or you can use ~ 3/4 cup laundry detergent). Let this sit overnight. Rinse off in the morning and dry. You’re good to go!

These are some good methods:

Try Easy Off Cold Oven spray. Remove the racks, take outside, place on newspaper and then spray the racks. Let sit for while and then use a plastic scrubber to remove the residue. Hose off.

I tried the same method used for oven grates. Remove racks from oven put in large plastic bag. Poor in about 1/4 cup vinegar and seal bag. Let sit overnight. Then wash with hot soapy water. If racks are large I’ve found ziplock to have large bags used for storage that work well.

I put mine in a large plastic bag, take it outside, then spray them with oven cleaner. Let it sit for a hour or so then rinse them off. The gunk should come right off. It works better if you do it on a warm day and let the bag sit in the sun.

I line the bathtub with old towels (to prevent the tub from getting scratched), sprinkle generously with baking soda, add 1 cup of white vinegar (you can even use cleaning vinegar which is a bit stronger), fill the bathtub with HOT water to cover the racks and let them sit overnight. They should just wipe clean. If there are burnt on spots that need a little extra scrubbing, use aluminum foil to avoid damage from steel wool. Sparkling clean!