Your eyes focus through muscles which make tiny adjustments to the lens of your eye. These muscles are just like any muscle that gets over or under-used. The underused ones get weak while the over-used get tight and can't relax.
If you think about what we did until about 100 years ago, we where scanning the horizon, or making tools, throwing things, etc. etc. This meant lots of changes to the muscles. The muscles relaxed to allow us to see far away things, and tightened when we needed to focus on things near our face.
Now, we spend most of our time looking near distance, and very little time on medium to far distance. So the muscles are constantly engaged which leads to tightness which leads to a constant reshaping of the lens. Because we are not used to relaxing the right muscles and tightening others, we end up with myopia.
I started working on this myself years ago, and I definitely notice a difference if I am working too much and not getting outside enough. So as ascuttlefish mentions, get outdoors.
But when you are outdoors, there are a few tricks I rely on. #1, I assume you live in a city. Don't walk around looking at the ground. Try to pick out far away things. How far can you see. Try and work your eyes in ways you don't currently.
I spend some time trying to read a sign as far away as possible.
Driving isn't good for your eyes, as you probably don't realize how much time you spend focused on the back of the car in front of you. This is not long distance. But I wouldn't work on your eyesight while driving, let's just keep everybody safe.
I find cycling (and particularly mountain biking) to be really good as you are constantly adapting to looking up the trail as far as possible, and taking quick glances at what is right in front of you. Very challenging for your eyes, particularly if you are just starting out (lots of people only look right in front of them, and they can't go as fast). The same can be done with trail running.
Make a game of it if you can. I'd like to say that I step away from my computer every 5 hours or so for about an hour, though there are definitely times that I'm unable to do that.