Since this product is hard to remove, we recommend using an oil-based eye makeup remover. Please insert it into the holder of the "Maquillage Perfect Black Liner BK999" (sold separately). (1) Remove the cap and turn the holder to remove the tip from the main body of the container. (2) After removing the used cartridge from the tip, firmly insert the silver ball end of the new cartridge into the tip, ensuring there are no gaps, and then insert it back into the main body of the container. (3) With the brush tip facing downwards, press the push button all the way down and hold for about two seconds. Repeat this process about ten times to thoroughly distribute the liquid throughout the brush tip. (The number of pushes may vary depending on how you press.) *It may take some time for the liquid to be distributed throughout the brush, so be careful not to press the push button too hard. When using for the first time, or if the brush tip is cracked and difficult to use, press the push button several times to thoroughly distribute the liquid throughout the brush, then smooth the tip with tissue paper before use. If the line becomes faint and difficult to draw, put the cap back on and shake the container several times. Then, remove the cap and press the push button several times to fully soak the brush tip with liquid before use. If you use it over eyeshadow, it may cause the liquid to be difficult to dispense, so we recommend using it first.