The body of the lighter is normally stuffed with cotton wool, designed to absorb and hold lighter fuel (petrol) which feeds up into the wick. You pull off the outer casing which should reveal the cotton wool. You then pour in petrol until the cotton wool is well damped, reattaching the casing when finished.
If access to the cotton wool is through a screw hole in the bottom, you remove the screw and proceed similarly.
Derek Davis