Already took dropbox appointment with old passport number, need to change it new passport

I booked my US dropbox appointment in chennai/India with old passport, I got new passport renewed, I want to get the stamping on new passport. Please advise if any has done it before recently with process.

You can submit another DS-160 with new passport # and link the new DS-160 in the CGI portal from where you booked the appointment or simply call VFS and they can linkbthe new DS-160 with your appointment.
When you go for dropbox carry copy of old and new DS-160.