You can delete the data of multiple users at the same time by navigating to System > Settings > People and Activity > Bulk Erase Users. Here you can select which users you want to delete by selecting the checkbox next to their name within the ‘Users to be deleted’ panel. You can also use the calendar found under Cutoff Date to filter out users who have not had a lesson since that date.

The Bulk Erase Users page

Note that the Submit button will not appear until the ‘I confirm that I want to irreversibly delete data for these users’ checkbox has been ticked.

Additionally, you have the option to select these users individually or simply ‘Select All’ to select all users on the list.