If what you have is a cartomizer, then there is a white soft, flexible cap on the mouthpiece end. Remove that with a paper clip, and you can add up to 20 drops or more into the filler in the cartomizer. Add a few drops at a time so that it will soak in, and tip the cartomizer a little so that the liquid does not just go down the center hole.
If it is an atomizer/cartridge, then the cartridge and atomizer can be separated. At the end of the cart that goes into the atomizer, you will see a white fiber filler. You can either push the filler aside a little bit with a straightened paperclip, and add drops of
eliquid until it is wet on the top, or even remove the filler with a pair of tweezers, add
eliquid into the cart to just below the rim, and then reinsert the filler with the tweezers or with your fingers. Then add one or two drops just to wet the filler on the top.