Reschedule Visa interview (US immigration)

[speed0002]

I'm a US citizen and the petitioner for my parent. My father got a Visa interview letter from US embassy in Mumbai stating interview date of next month. Now, he has some work to finish before he appear for the interview.
What is the procedure to re-schedule immigrant visa interview date for a lter date?

(I know the fact that after getting visa he can stay for 6 months in the country)

Did somebody has any information to share?
regards

[joseange]

hello

thanks for approving my registration!