Configure Lobby Settings
Depending on how a meeting is set up, the meeting organizer can allow participants to join automatically, or wait in the lobby until they are allowed to join.
Note: If the meeting is configured to have participants wait in the lobby, no participants are allowed to join until the meeting organizer arrives and allows them to join.
For complete documentation on configuring Skype for Business meetings or Skype for Business client settings, see the Microsoft documentation.