As far as I know, it is not possible. But on YouTube, they say @ (Username) and they get an E-Mail saying what your reply is, but I'm not sure it works on Fanfiction.Otherwise, you could give them a...
We use "How do you do?" when we meet someone 1st time. It's used as "Namaste".
the reply of 'Namaste' is 'Namaste'. then reply of 'How do you do?' will also be same (How do you do?)