You can churn a customer by navigating to Customers then going to the customer you would like to churn. On the Details tab you will see a churn date. Setting the churn date will mark that customer as churned. Note: churning a customer will not churn the individual subscriptions for that customer.

To churn a subscription go to the Customer, then click the subscription you would like to churn. Click Churn date to set the date the subscription churned.

Subscription churn data will be available in the MRR Churn and SaaS reports.