Turn the metronome upside down so that the bottom is facing toward you. Push aside the small bracket that keeps the panel to the bottom sealed. Place the head of the screwdriver into the side of the panel and gently pry the panel open. You can now see the gears and the large static weight attached to the bottom of the pendulum.
Coat the gears with a small amount of WD40 (or similar lubricant). Spray the lubricant where the winding mechanism is connected to the gears.
Wind the metronome slowly, while observing the gears. The WD40 should be enough to loosen sticky parts that are keeping the pendulum from swinging. If the metronome does not wind easily right away, wait a few minutes for the lubricant to seep into the parts. If the gears still don't move --- or if they are obviously broken --- you will have to replace the entire mechanism. If all is working, replace the panel.
Place the metronome on a flat surface.
Turn the winding mechanism clockwise four or five times (do not over-wind).
Release the pendulum from the tab at the top of the metronome (this tab keeps the pendulum from swinging). Set the tempo weight within the range of 208 to 192 ("presto," meaning speedy) beats per minute. If the pendulum is not swinging (and the mechanics are indeed working), put a piece of paper under one side of the metronome; adjust the thickness of the paper by folding it over until the metronome is balanced and the pendulum is swinging evenly.