To lock or unlock an existing meeting room, follow these steps:
- Visit the meeting room
- Click on Share at the bottom
- A box will open: here you can (un)lock the meeting room.
To lock the room, make sure that the public link shows as 'Should knock'.
To open the room, change the setting of the public link to 'Can always join'.
This help article gives more information about the sharing settings of meeting rooms.