It is very difficult thing to do. There are very excellent and very real completely logical reasons to be misanthropic.
However, I think that the only thing that ever countered it for me is when I hung out with groups of people with great attitudes.
For example, I joined a hiking group, and we went out and hiked twice a week. I noticed that the people there were upbeat, because going out to hike in nature seemed to attract people who are upbeat. I so much enjoyed those hikes years ago.
Then last year I joined a tech group that was very personal and everyone knew each other and very helpful and friendly.
But I have also joined groups that suck and I hated them and everyone in them.
So my solution to you is to go to a lot of group meetings and find one whose people you like. Don't stay at groups you don't click with, that is folly.
If there are no groups around, start one of your own. Advertise on meetup.com, craigslist, etc.
And, it is an "in person" kind of thing, not done over social media. Nobody should be allowed to fuck with their smart phones should be a rule - you have to interact with each other.
But, you have to make the effort. It's work. But it is rewarding, if you end up with a group of people that you like.
Also, constant and consistent vigorous exercise helps a lot. Exercise releases all kinds of chemicals - endorphins, dopamine, etc and it makes you feel better about yourself and others. And when you are in great shape, other people get a second sense that you are physically in shape and you let off some kind of pheramones or whatever, maybe have micro-non-verbal communications that let people know, and they like you more.
That's probably why hiking groups are the best. Everyone's endorphins are being released at the same time and it creates a feedback loop within the group, and everyone gets along. This isn't a guarantee, just more statistically likely, I think.
Good luck.