Change the assistance information
I can't find the form where I can change the assistance information (with a phone number field) -- I don't know the English page name; in French it's "Prise en main".
Re: Change the assistance information
The Getting Started page was an option available in the old Flash version of the Home page of Connect. When on Home click the option to "View the old experience" at the top right of the page (below the search bar). This should expose that option for you.
However, I don't think you can change any phone numbers there. You may be looking for the Audio Profiles option under the My Profile tab. The other place I can think to modify phone numbers would be to go into the Edit Information section for your meeting room. There you can change the audio profile linked to the room.