How to change “Devise: password reset instruction email’s subject”

you can change it in devise.en.yml file in intilizer directory

And set your own subject for any mailer

                   mailer:
                     confirmation_instructions:
                       subject: 'Confirmation instructions'
                     reset_password_instructions:
                       subject: 'Reset password instructions'
                     unlock_instructions:
                       subject: 'Unlock Instructions'