In a Demodesk meeting, simply open the participant list. There, go to the row of the participant that should be able to share the local desktop and click on the "Request customer desktop share" button.
Immediately, the participant will be asked to share the local desktop. They can choose between sharing the entire display or just one application window, whatever they prefer. At any time, the participant can end the screen sharing, but also the host has the option to end the sharing or switch to a different tab.
IMPORTANT: Customer side desktop sharing currently only works if the participant joins the meeting via the latest Chrome or Firefox browser.