Currently it is not posssible to delete old onboarding and other checklists (it is still offered in drop down menu when HR user is managing his/her processes). The only way is to delete all related Worker actions and remove the checklists in all Workers where these checklists have been referenced.
I´d like to suggest to have possibility to delete old checklists without deleting the Worker actions or to have possibility to archive old checklists. It would help to keep the system clear for users.