How to Send Password Forget mail to User upon activation of Account in Rails

In our Application Users are created by Admin with a Random Password . So we send Activation Mail to User (http://localhost:3000/users/confirmation?confirmation_token=1xxxxxxxxxxxxxx")
We Use devise_for :users

def confirmation_required?
    true
end

So now We want when User activate his Account then automatically they send a Password Forget mail to him on his mail ID