The reason for skipping leg day is that my leg muscles are decently
developed , hence I don't target them specifically.
Honestly I'd doubt that. Your "leg muscles" consist a large variety of muscles. The obvious ones like your quads and hamstrings are there, but I don't know how you can say that your iliopsoas is sufficiently strong and flexible. Also, it's quite difficult to strengthen your lower back and abdominal muscles without engaging your hips, which in turn engage your legs.
I would like to change this schedule into a 3 day program. How do I go
about it and what all compound exercises do I incorporate for each
body part ?
Compound exercises, are by definition, not concerned with each body part. I would encourage you to look into one of the numerous highly effective strength training programs out there.
For the most part, these will use squats, pressing (bench and overhead), deadlifts, and rows (or cleans). It might field weird to ditch the classic isolation and body part split routine that you're doing, but take heart in the fact that there's simply no way you'll be small and squat twice your body weight. You'll be powerful, big, balanced, and spend less time in the gym.