Resets are in the product manual as well as setup.
The one setup that always seems to give trouble is HDMI ARC. I try that but then move to other connections fast.
Out of the box the 6400 worked fine with our Panasonic sound system but after a few weeks, the TV did a system update and now even though it connects with the sound system, there's no sound. Is there a way to do a system reset so the TV will work with the sound system again?