If you are still having issues, also try the builtin email reminder that sends emails reminders. See https://phpeventcalendar.com/docs/event-emailpopup-reminder/ 

The easiest way is to use cPanl Cron job. See https://kb.iweb.com/hc/en-us/articles/230244168-Setting-up-cron-jobs-with-cPanel-

When use PHPMailer, you must set up an SMTP server to send out emails. See https://github.com/PHPMailer/PHPMailer