How to apply H4 for infant? Dropbox option?

We both have approved H1 and H4 visas. My wife is now in India with our newborn and need to apply H4 for our kid. Please let me know the process. Do we have to go to Consulate for interview or is it just dropbox for kid?

You can use dropbox option.
You can start to fill out DS-160 and then book appointment like normal. When you are trying to do that, it will prompt you for the dropbox and should get that option before you go for appointment.