To adjust headlight beam (up/down) on Gen1 Prius you need a fairly long #2 Philips screwdriver, insert throught the Dime size hole. Insert in the guideways until it mates with the "cog gear". As you turn the screwdriver the beam should move up or down, depending on which way you turn the screwdriver. The photos below from a passenger side headlight (off the car) will help make more sense of the procedure.
