H1B approved; Procedure for obtaining my wife's H4 Visa?

I am currently on F-1 (OPT); My H-1B got approved two weeks ago; My wife is in India; I plan to travel to India in September to change the Visa status and bring my wife back. How and when do I apply for my wife’s H-4 Visa?

Your replies will be appreciated. Thank you.

Apply together for H1 and H4 visa in india