You may not need to disassemble the switch more than taking the back off it. Headlight switch button removal may not be necessary. You may just need to spray some lube at three spots. (I prefer aerosol silicone spray lube but you can resort to WD-40 if you have to.)
To start with, it helps to understand the how the "flash-to-pass" high beam return spring mechanism works. It's pretty simple.
Under the switch button there is a spring loaded rotating white lever.
There are two ribs under the bottom half of the switch button that it pushes on in order to return the button to the middle position.
What I would try first:
1 - Remove the switch from the clutch perch. There's a small Phillips screw at the bottom center that holds the switch to the clutch perch. It can be sticky so use a good screwdriver and apply lots of pressure to initially break it free. If you don't then you might strip the head of the screw.
Since there are several small screws involved, I recommend removing the left combo switch from the bike and doing this off-bike. If you choose to do it on-bike then consider doing it above a shoe box or similar to catch any tiny screws.
Now you need a very small Phillips screwdriver.
2 - Remove the turn signal and horn buttons: The turn signal button is held on by a small Phillips screw in the back. Once this screw is removed you can wiggle the button out to slide it out.
The horn button is held on by a small screw that can be accessed via a hole inside the back of the switch assembly. It's easiest to to do this if you depress the horn button while removing the screw. Note the spring and rod where the horn button mounts. (When putting the horn button back on the long end of the pin goes into the switch, the short end goes into the spring in the button.)
3 - Remove the 5 screws that hold the switch together: There are two different types of Phillips screws used. The short one goes in the top as shown here.
Now the switch subassembly will come loose from the housing.
4 - Spray some lube up under the bottom of the switch button at the base of the white lever. (If the white lever is not there then you'll need to replace the combo switch.)
5 - Spray a little lube at these two points in the back of the switch.
Now test the button to see if it returns better.
