A power interuption causes it to revert back to stock setting. The button sets the display brightness and allows for setting changes to the "aggressiveness" as well as learning the gear positions. Refer to the owners manual for the procedures on both.
You want to make sure it's on setting 3 for the most timing advance in all gears affected.
Setting 4 puts 1st gear back to stock. It is NOT the most aggressive setting!
Setting 4 works well on slick surfaces like rain to reduce engine power in 1st gear only. Just remember that second gear is going to hit HARD if you happen to be accelerating hard.
Skip its not a "reset" button, I just realized what you were thinking. The button is for changing settings, get your user manual back out and its in there. The installation part of the book uses the button during the install to set the gear position indicator, I see now how you misunderstood what it was for. You deffinately should go through the tests in the book to make sure its on all the correct settings.