There are many vibrations you can use, THURISAZ is very powerful but works really well.
For a milder vibration to start with use THOTH or THAUR if you want something in between.
Vibrate any of these mantra's into the third eye for 108 times, if 108 is too much you can do 36 vibrations to start with. 72 or 81 work well too for something intermediate.
After this breath in white golden light to your third eye for a few breaths. Feel the energy saturate your third eye and make it spin, expand and glow bright with white golden light.
Then meditate on it for a few minutes and feel it open. This will very quickly activate and empower your third eye.
HAIL SATAN!