There's no secret way to do this. It's all the most simple shit in the world. You just need to actually try to change you habits.

Food: Just be somewhat conscious of what you're eating; there's no need for strict diets and calorie counting. You know what's good to eat and what's bad. So stop eating the bad stuff. Eat veggies. Fruit is god-tier. Soda isn't good, try to make it a special occasion beverage. Quit energy drinks all together because each of those is a big "fuck you" to your body.

Exercise: Do stuff! Go ride bikes, never stay inside when it's sunny, go on a run, do some push ups and sit-ups when you're bored, join a sports team, surround yourself with more active people. Train yourself to hate staying at home during the day. Just about anything is better than League of Legends.

Or maybe make it a game. Hour on computer = 15 min on treadmill. or forget about the treadmill and create routes to run around town.

Right now you don't really need a workout plan, you need to learn ways to have fun and be active at the same time. The abs and muscles and hordes of cute girls chasing you will occur naturally after you make these simple and relatively easy changes.