First, you should learn more about LAANC — it allows users to request airspace authorization and to get approval in near-real time for much of the controlled airspace across the U.S.
Here’s a guide we put together that should help:
How To Get Drone Flights Approved in Controlled Airspace with LAANC
If you’re unable to get controlled airspace authorization through LAANC, you’ll have to request authorization through the FAA’s FAADroneZone portal:
Here’s a guide we put together that walks through that process:
How To Request FAA Airspace Authorization For Class B, C, D, And E Controlled Airspace: A Guide to LAANC and the FAA Drone Zone Web Portal