How to get H1B Expedited drop box appointment at chennai consulate?

I have a valid H1B petition and i’m eligible for drop box as well. I don’t see any open slots for drop box stamping, i’m monitoring every day at all 5 OFC’s.

Please let me know how to apply NIE for both drop box stamping and travel for me along with my dependents?

I have the recommendation letter from my employer explaining the critical business need.