Changing the message that users have to acknowledge before admission to a meeting room

[Janezo]

A few days ago, I found the feature that allowed me to write a message, that the user sees and has to click to acknowledge, right before being to a meeting. (I'm the Admin.) Today, I want to edit that message, however I haven't been able to find the place where I created it, to edit it. I've click around for hours. Please help with detailed instructions.