If you are a mobile user (Android) you are able to turn on your microphone and webcam if granted. Here is how.
USE THIS FOR ADDITIONAL INFORMATION
Enabling Microphone or Microphone and Webcam
- Click on the Kebab menu (see below) in your browser (upper-right) and then tap the "Desktop site" checkbox 

 - Now the browser will reload your webinar room
 - Ask the host to disable the permissions they provided and enable it again (if you were not using the Desktop site)
 - Click OK to the following

 - Now you will be presented with mic/webcam buttons at the mid-bottom area (it should be Gray until you enable it

 - Once you enable the mic or webcam the appropriate device will be enabled
 - Do not turn off the mic if you only enabled the mic as it takes away the permissions. Do not turn off both mic/cam if you enabled webcam as it takes away the permissions. Only do this when you finish or just let the host take care of it