[SDF- 84957] How to hide/exclude default instance for some users

[SDF- 84957] How to hide/exclude default instance for some users

Is it possible to exclude some users from the default instance called IT helpdesk, or to hide this instance for some users? Because I want to create some new instances, assign several users to them, and they should use only the content which is offered in these new instances.
Thx and BR