Some jams have a Discord; those are good places to find other people to team up with.
Joining a jam is very easy - go to the jams page and find one (or more) that fit in your interests and skill set. Some are open to any kinds of games; a lot are more restricted - specific themes, or specific game engines, or tabletop games only, and so on. Some encourage teamwork; some don't allow it.
Finding a good team for collaboration is likely to take some time as you get to know people, either in the specific game jam community area, or in Discord or similar places.