Technically only the project lead (who I assume would be you) needs an itch account to be able to enter and submit to any game jam. Should your friend make an account themselves, you should be able to add them as a Contributor on the game following these steps:
- Locate the game on your dashboard and click Edit
- In the More tab to the right, click the dropdown and select Admins
- Enter in their Username or Profile URL at the bottom and hit the Add Admin button
- Send the URL you receive to your teammate so they can confirm