Camera turning off mid-meeting

Hi - We are currently in a Zoom meeting, via our YeaLink device, that was set up and administered by someone else.  When we carried out a test the camera came on and we could hear the others. When we joined the meeting, the camera was on and we could hear everyone else.  Suddenly the camera went off and we could not turn it back on. We can still hear everyone.  Can anyone advise me what to do to turn the camera back on without leaving the meeting?

Thanks