The Customer Retention - Details report will allow you to view customers who have not returned to your studio after their First Visit.
Go to Reports > Marketing > Customer Retention - Details.
First, you will need to select the desired date range. This report will show everyone who has taken a class in the date range selected. If the 'Total Check-ins - All Time' column displays a 1, this means that the customer has checked in during that date range but for their first and only class.
Export the report and filter by the Total Check-Ins - All Time column for customers with 1. If you sum the rows after you have filtered, you will be presented with the number of customers who have not returned since their first visit.
It is helpful to look at the column called 'Last Check-in' to see the date for each customer relative to the current date you're pulling the report. That way you can determine if it makes sense to reach out based on how much time has passed since their first visit and try to get the customer to return with either a special offer or general marketing outreach.