Create a Cron Job for "email before download" wordpress plugin

I have a WordPress site with a plugin called "email before download". What this plugin does is that works with contact form 7 plugin and it captures your email before you download a demo software. This plugin sends an email to the WP admin and also saves on a database table the email of the persons who downloaded the software. What I need is to follow up on those emails automatically by setting up a cron that emails the user after 30 days of downloading date. The table dos not have a download date. so I need this to be fixed to a cron runs every day and checks if the software was downloaded more than 30 days ago. If so a email template will be sent to that user only once. After that user must not be emailed again. Just once. I think its better if the cron is a single php file I would not like to edit the plugin. Can this be done? thank you!