I installed Joplin Server on my team server, so I change the config of sync in the app client to the URL of Joplin Server with the Joplin Server Email and Password and that works well
Now I want to other members of my team can register and use this Joplin Server, how to do that ?
There was an environment variable SIGNUP_ENABLED=1 that used to add a signup option to the main page. I have not tried it since the early testing of the first versions of Joplin Server.
Also you speak of installing this for your "team". If you intended to use Joplin Server in a commercial environment you need to be aware that, unlike Joplin, Joplin Server is not FOSS and is subject to a personal non-commercial purposes licence.
It's not for me to say. Only the owner of the Joplin Server software ("the Licensor") can licence the software for other than personal use.
I am not a lawyer and the reason I mentioned it was that people seem to often assume that Joplin Server is FOSS like Joplin. I felt that you should be aware that if you were using it in a commercial environment you may later find that the software was being used without a licence to do so.