While it is easy to refill the Canon PG-740 Black Ink cartridge, we do recommend you check out original inks from Canon. And if you decide to refill, you should make sure that you know exactly how to do so. First of all, you need to remove the ink cartridge from your printer. Then, open the ink cartridge and shake it gently to release any excess ink. Do not shake the cartridge too hard, as this can break it. Once you have done that, replace the ink cartridge with a new one.
There is a little hole at the top of the ink cartridge. Use a needle to puncture the plastic and make a small hole. Then, use the thumb drill to make a larger hole. After that, you can insert a syringe to check the size of the hole and whether or not it is large enough to hold the ink. Afterwards, you can insert another cartridge.