Adding individual users to a chat channel in Odoo

I use Odoo 14.0 .

I created a chat channel for all my Odoo users.

Still, not all user can see this channel, and I do not find an add user button in the channel administration.

https://www.odoo.com/forum/help-1/chat-in-channel-not-displayed-158887

says that with some SQL magic I could solve this but I do not have access to the database. And at all, this should be an easy thing to manage the users of a channel.

How can I do this in Odoo?