This info is listed on the wordfence assistant plugin page:
"If you have been locked out of your WordPress installation, we provide a user-friendly way to unlock your site by sending an unlock email to the site administrator's email address. Occasionally this does not work which is why we created this plugin. In this case, you will need to delete the Wordfence files from the /wp-content/plugins/wordfence/ directory. Once you've done that, install this plugin and use it to disable the Wordfence firewall. You can then safely re-enable Wordfence and adjust the onfiguration to avoid getting locked out again. Make sure you update your administrator email address to that you can use the user-friendly email unlock feature if you lock yourself out of your site in future."
You can delete the Wordfence directory through an FTP client like FileZilla or by using the file manager in your site's cPanel.