Hi, Thanks for your question.
Actually, you still need to submit the game to the jam as an individual, but you add the team members later.
To add team members for your game, go to your game page -> Edit Game -> Admins (send them an invite by adding their itch io username URL, then click add admin).
After they have accepted the invite, click the checkbox that says "Display as Contributor".
Your other team members will then now show up as contributors.