try some team sports/sports with other people, like tennis or football (something you are interested in), and decide on specific days you can all do, or join a club. As it will be more varied and you see people it will stay interesting and fun.
Or plan a route outside, and walk/run/cycle it, and plan to do a variety of routes each week. Start off with some fairly short routes, and when you are used to it and it is part of your routine maybe build up with some slightly longer ones. Don't go over the top though as you might bet injured or get some other health problems. If you are walking or running maybe find some podcasts that you enjoy to listen to (but remember to listen out for other people/ traffic)
or get a dog so you have to take it out for walks aha
or try a bit of swimming and decide on a realistic number of lengths to do, or treadmill/gym stuff etc and decide a distance/time/number of reps (e.g. See how fast you can run 3km, or exercise bike for 10 mins) and then just go and do it
it might be hard for a few weeks but soon you will feel yourself getting fitter and that itself will be quite motivating.
And once you've done it, do something as a "well done" that you look forward to, i like a good vending machine snack. Or plan to do something fun later on in the day
also remember that with exercise you will need more food, make sure you get enough protein and carbohydrates and fats as your body needs them to build muscle and to recover and to have enough energy for the next exercise you do