This option works in premium version of the plugin only.
- Using tab Filter filter necessary products to be deleted. Also you can use checkboxes which has higher priority in the selection
- Then go to tab Bulk Edit and check there checkbox 'Bulk deleting'
- Press button 'Delete Products!' and wait until operation is done
NOTE: Make backups before such operations as History doesn work in this case, but deleted products (not variations) you can always find in woocommerce trash been (wp-admin/edit.php?post_status=trash&post_type=product) if it will be necessary.