In order to restrict access to a previous prospect/customer/company (that originally was granted access):
Click on the Share button in the top right hand corner of your room.
Change the permission level to 'only permitted users and companies can enter'.
Click on the 'edit permitted users and companies' and type in the name of the people/companies that should have access.
In order to choose users - type in their email addresses
In order to choose a company - type in their domain e.g.teamaligned.com