For removing the logs from your database, you would need to deactivate and delete the plugin from your website.
Before deactivating the plugin, you have to enable the option “Remove Database at Uninstall” under General Settings of the plugin.
This will delete the existing email logs from the database. After that you would need to reinstall the plugin on your website.
Please note that Remove Database at Uninstall action will also remove your existing configuration and you have to reconfigure the plugin with your smtp details.
Thanks & Regards.