I’m pretty hopeless at this too, but if you’re still in school (like I am) and happen to be in some of their classes, speak out more and just try harder to be good at the class? Or stand out somehow. I guess then it would be easier for him to ask to be in your group or for you to be accepted into his group if you ask. And you can work from there, or even just talk to him about the subject.
If you’re not in the same classes, you could still be like: Oh, we had really difficult homework yesterday in Math, did that also happen to you etc.
I’m pretty introverted irl tho so don’t take my word that this will 100% work!