In the Pro version of our plugin we have options to limit the number of entries to one per user/IP address/cookie, but I’m afraid we do not have any similar functionality in the free version of our plugin.
We aren’t allowed to answer questions about the Pro plugin here, so if you would like to find out more about this, could you please open a ticket in our helpdesk here? https://formidableforms.com/new-topic/
Best,
Nathanael