To delete Customers individually:
Navigate to Contacts screen > Customers table and choose a customer to open a customer card.
Click on the 3-dots at the top corner of the customer card and select Delete from the drop-down menu.
To delete Customers in bulk:
Navigate to Contacts screen > Customers table and check the boxes for customers you want to delete.
A Bulk actions menu will appear at the top left of the table. Click on it and select Delete from the drop-down menu.