Contacting Customers for a Specific Register / Date
There is a 'Contact Attendees' button at the top of every register - this will give you all the phone numbers and email addresses for customers attending a particular class on a specific day.
For example - this 'Contact Attendees' button would give me a list of 10 email address and phone numbers.
Contacting Customers for a Regular Class
If you need to contact everyone that e.g. is attending your Tuesday 10am class over the whole term, then you can retrieve the email addresses for all of your customers by downloading the 'Sales CSV' for this class.
This will give you a full list of your customers for the whole term, grouped by each event date in that series.
If your customers have booked in for multiple classes, then there be duplicates in this list. To de-duplicate this list:-
If you're using Excel, select one of the email addresses and then click 'Remove Duplicates' under the Data Tools tab.
If you don't have spreadsheet software, Google Sheets is free and easy to use. Simply copy your list into the first column of a new sheet, click into another cell and then type =UNIQUE(A:A)
You can now copy the email addresses to contact all of your affected customers via email (remember to use BCC!).