Here’s a detailed video from iRepairMD that shows how to replace the Mavic Pro gimbal ribbon cable (from start to finish):
Note: The DJI warranty states the Mavic warranty could be voided if any work is done by a non-authorized service provider (which includes yourself). If that’s not a risk you’re willing to take, then you should send your Mavic to a DJI Service Center or authorized service provider instead of attempting to do the work yourself.