Yan, Leo gave you some very good advice. Bonsai is usually seen as a solitary hobby, done alone, but it’s even more fun with friends. Especially when working with large material!
The collaboration, exchange of ideas, helping hands all make for a great experience for everyone.
Repotting can be a physically challenging activity for older people, and for those with larger trees. Several people working together on a tree makes the work easier and faster.
So... offer to help to repot! You don’t actually have to know anything! Just do what the experienced person says to do.
As an example, when repotting, once the tree is removed from the pot, the first thing I do is work the bottom of the rootball with the three pronged scraper that looks like a fork with curved tones. To get access to the base of the rootball, I tilt the tree over sideways 90 degrees. The branches hang over the side of the work table. On smallish trees, I can hold the tree in this position with one hand and work the scraper with the other. On a big tree, I can’t. It’s best to have someone else hold the trunk of the tree to keep it from falling while I work the root ball. In my case, I can get my son to do that.
My point is, by volunteering to be a “helper” you can learn how the experts do things.