Just start out small, like a single walk maybe 3 times a week. Set a reminder on your phone to prompt you cos it's not in your routine atm. Don't be mad at yourself if you forget or whatever. Just say, oh well I'll try again tomorrow.
If you don't feel like it, you can try trick yourself into it. Like get your shoes on and just walk to the footpath. Now you're there and ready, you may as well keep going for a small walk anyway.
It takes 2-3 weeks to form a habit. That's the hardest part. After that it becomes easier :)