My own advice is to join an organization, volunteer program, club or class, and to go to free events in your local area^[This footnote is a bit late but please be aware of mitigating COVID.]. At least speaking for myself, the problem with social interaction is mainly just the unpredictability, right? So the best "hook" to build social skills from is going to be the more predictable social interactions, or at least the social interactions that "feel" more predictable and less risky. This can be something like a support group for your form of neurodivergence, sure, but it can also be a wide range of other things. Lately I've liked talking to old ladies, for instance. If you're struggling even talking to cashiers, librarians, and train conductors, then you start there.

Some other things to note is:

1. There's talk sometimes of asocial people getting "adopted" by someone who's very talkative and extroverted, but the fact of the matter is that you can yourself be the adopter. You are not the most asocial person in the world, there's going to be times when you aren't even the most asocial person in the room. And in those times, you can be as weird as you want to that person, because what exactly is that person going to do?
2. You can "fake" confidence to some extent. Being an overseas American has actually been kind of helpful to this end because I can play into the rootin tootin yeehaw stereotypes/clichés, and play into the ways I already end up standing out — although that is also obviously something you have to be a bit careful with. But yeah, picture yourself in the third person as someone more confident and try to act as that person would. Fling the door open like Cosmo gotdang Kramer and say something silly. Do a silly voice. No-one's going to stop you, and eventually the "fake" confidence just becomes actual confidence.

Ganbare biimu!