Only via an estate agent who lists their instructions on Zoopla. You can find such estate agents via the "Find agents" tab, or ask your preferred agent to contact Zoopla to arrange this if they don't already do so.
Unfortunately there is no facility for private listings. If you would like to advertise your property on Zoopla we would suggest contacting a local estate agent who is registered on Zoopla and instruct them to sell / let your property. You can search for agents using the 'find agents' tab