Turn Instant Pot to saute setting. Add oil, turkey, onion, and bell pepper to the pot. Cook until browned breaking up the turkey as it cooks. (Pour off any grease if using ground beef.)
Turn off the pot and add ranch dressing mix, taco seasoning, and corn. Pour in tomatoes, Rotel, pinto beans, and chili beans with the juices from each can. Stir to combine.
Lock Instant Pot lid in place and set steam valve to sealing. Turn pot to high pressure (Manual setting) for 8 minutes. Once cooking has finished, let naturally release for 15 minutes. Carefully quick release any remaining pressure.
Open lid and stir soup. Season with salt and pepper to taste. Serve warm topped with crushed Doritos, sour cream, cheddar cheese, and cilantro if diesred.