Resetting plugin (not creating accounts)?

I set up Opt-In Panda to add emails to an email and automatically create WordPress accounts for emails signed up. It initially worked but no longer sends set password/account creation emails when Mailchimp is enabled and adjusting settings does not appear to fix this. I have tried uninstalling, deleting and reinstalling the plugin but it retains settings when reinstalled (and account creation does not work).
Is there a way to completely reset the plugin/delete all settings and associated files to do a fresh reinstall?