You dont need to do anything. All e-tickets that remains in Waiting List after chart preparation, will get cancelled automatically and the amount will be refunded to the Bank Account/Credit Card that was used to book the ticket within 5-6 days, normally.
And wait listed e-ticket holders cant board the train, as their tickets are cancelled after chart preparation and if found boarded with a wait listed e-ticket, they will be considered as travelling without ticket and will be fined accordingly