|Note: Make sure you are logged-in and in the correct event|
This feature is still in beta, however it can already be used to delete a certain group of participants. They can be grouped according to the default or custom fields of the "options" type.
Go to the Labs page and then click on "Mass-delete."
Then choose the corresponding field and grouping value (e.g. all the "Speaker" participants).
Finally, click on delete. The selected participants will be scheduled for deletion.
Take into account that it may take some time for large amount of participants.