The quickest way to create a once off reminder is to click the appropriate follow up badge before completing the job, if this won't work for your business this lesson will show you how to do it manually.
Click New Recurring Job
Search for and select a customer
Enter a description of the reminder
Select Daily, Every 1 day
Set the date you want to be reminded
Set End after 1 occurrence
A reminder will now appear in the inbox one week before the date selected, ready for you to contact the client to arrange a booking.