If you have a pullup bar at home, then you can work every muscle in your body with just pullups pushups, and squats. Pullups work your biceps, posterior delts, and back - pushups work chest, abs, triceps, and anterior delts - and squats work every single muscle in your legs. You can also add in crunches, or flutter kicks as a fourth exercise for your abs. for the pullups you want to do a nuetral grip pullup ideally because that wont neglect your back or biceps: this is a great video on pullups you should watch: https://www.youtube.com/watch?v=iqwaby3dZxU the squats will need to be weighted to be challenging. This is a small enough number of exercises that you can fit it into a full body single day split. the only problems is that this full body split neglects lateral delts which youd need a lift like shoulder press or lateral raise to work, but its a minor flaw in a pretty good workout split. hopefully that helps you get back into shape