Aldous Huxley swore by the Bates Method (https://en.wikipedia.org/wiki/The_Art_of_Seeing). I went through a period where I tried it and it did seem to help, but YMMV, not scientifically-proven, etc. etc.

I will say that the people with the best eyes I know (one was a fighter pilot, and still has great eyesight into his 70s) spent a lot of time outside tromping through the woods and read a lot -- so had a habit of switching back and forth between close-reading and far-gazing.

Whether it helps or not (and I believe it does, when I forget for a few days, my glasses seem too weak), it isn't the worst idea to look up from the phone or laptop and focus faraway a few times an hour.

I don't know if you can fix presbyopia, though...I think that's something that just happens like clockwork at 40. :/