Hello!
If the Yealink is in the Zoom meeting that's hosted on the Attorney's computer, when the A20 needs to not be in the meeting, he could move it to the waiting room from his computer. This way, the A20 is still in the meeting, but cannot participate in the call. Then when it's time for the A20 to rejoin the meeting, it's easy to admit them from the waiting room back into the meeting.
Hope that helps and please make sure to mark the solution as accepted if this information is what you needed.
Thanks! Rick