You can send email reminders to customers from 2 places:
Here's how to do from Scheduling:
Click on 'Send client reminders'
Choose the date:
Click on 'Click to search jobs', check the jobs you would like to send reminders for and click on 'Send reminders'
Make sure your templates for customer notifications in Settings -> Templates are filled out as per your need!
If you need help just email us - firstname.lastname@example.org