The screen share green box is stuck to the bottom of my screen

I use Zoom workplace to give online classes.  I use the Advanced Screen share - part of my screen regularly.

That is the green box which comes up to share just what you want to share from your screen.  I moved it too quickly the other day and now it is stuck to the bottom of my screen and I can't reach it to pull it back up.

What do I have to do to get the green box back into the middle of my screen when I share?

Many thanks, Farah