I will tell you how . It is not very easy .
First of all you will need patience .There are three methods for opening of the third eye .
Method 1 :
Lay down in bed with eyes closed .Focus your sight at the center between your eyebrows .You must look at this point for two hours in order to open your third eye for 2 years .You will feel a bit of a headache but do not worry .
Method 2 :
Light a candle and gaze in it for 20-30 minutes . Just look and don't think for anything .You should open your eye for 2 or more years with that method given by Osho .
Method 3 :
Sungazing. Each morning around 5 o'clock when the sun rises look at it for 5-15 minutes .30 minutes when 1 month passes .