Once I create and test it, how can I clear my survey data and start fresh?
There are two options:
You can create a clone of your PollUnit in the "My PollUnits" section. This does not yet work for PollUnits about images.
As a premium user You can delete entries from Your PollUnit: Visit the admin link of the PollUnit and click on the clear icon next to each participant.
It is now also possible to delete all participants from a PollUnit. As admin and premium user you can click on "Delete all participations" in the context menu (three dots).