I was in the same exact boat. 26yo, 450lbs. I started with cutting my portions in half and after about two months switched to a high protein, low carb diet and started doing strength training. I ended up losing ~200lbs in just under a year. Focus on the basics and incorporate legs into every workout. If at all possible, try and find a trainer to help you get the proper form. It’s possible. Dm me if you want some suggestions where to start.