You can set Apple TV so that Conference Room Display mode is locked until a 4-digit passcode is entered.
Open Settings
on Apple TV.
Go to General > Restrictions, and enter the passcode if required.
Make sure Conference Room Display is set to Restrict in the list of restricted items. For more information, see Restrict access to content on Apple TV.
Note: You use the same 4-digit passcode you set in Restrictions to unlock Conference Room Display mode. If you forget the passcode, disconnect Apple TV from the power outlet, reconnect it, then press and hold the Back button
(second-generation Siri Remote) or
button (first-generation Siri Remote) as it restarts. This temporarily unlocks Conference Room Display mode. For more information, see the Apple Support article Manage AirPlay settings on your Apple TV.