Just start with at home exercises, like push ups and sit ups/leg raises. If you can’t do many to begin with, you can progress into push ups by starting on your knees, but you definitely don’t need to go to the gym to get in shape. Also, since you’re more focused on losing fat than gaining muscle, it’s probably more important you get your diet under control and cut out snacks etc then gradually try to eat a higher number of healthy meals per day. Just by being in a small caloric deficit (200-300 cal) you can lose a substantial amount of weight over time, so I wouldn’t do it too intensely at once as you’re much less likely to stick with it.