OK, figured it out.
The post on the Benelli forum unfortunately doesn't explain anything.
This will work with both the NOVA and the M1.
Here's what to do.
Take out the trigger housing.
Relieve pressure on the safety button if desired by drifting out the solid pin just behind and above the trigger.
Drift out the roll pin at the top of the trigger housing, the one behind the trigger and directly above the safety button.
Watch out, or put a piece of tape over the hole at the top of the housing (look down the hole to see the roll pin running across) so you don't lose the spring which holds the detent pin. It will fly out as you drift the roll pin.
With pressure from the detent pin removed, reverse the safety button.
Next, insert and compress the detent pin spring with a punch while drifting the roll pin back across the channel (it's a three hand job).
If the roll pin doesn't seat all the way (I hate roll pins), just get it most of the way, or replace it with a piece of solid drill rod if you have the right size. (And if you removed the solid pin just above the trigger, press the trigger back slightly and replace said pin.)
You're done! Reassemble the gun.
