There is a lot already written on this. However, Not sure if you have a
Smart Controller or standard Controller, but update should work for both and Drone.
Make sure you have the latest version of DJI Assistant 2 for Mavic (Download from DJI site 2.0.8 is latest)
Make sure you don't attempt to update over wifi, it odds are will not work
Use a USB-3 cable (one with Drone) and use a USB 3 port on your computer
The Drone and Controller both need to be updated. Both will connect via USB-3 to a computer and update accordingly.
Update needs to have a good wifi or ethernet connection on Computer.
Process takes a while, between 10 and 15 minutes depending on your connection speeds.
Paul C