Toner refill, while very cheap, can be be very risky for the printer life as well as for your health. It is quite complicated to do a toner refill especially if you do it for the first time. In addition, you may inhale toner dust in the process of refilling it, which is very bad for your respiratory health.
My advice is to just buy a compatible toner cartridge. In Australia, I buy an HP compatible toner for my laser printer in the Thrifty ink website and the cost is almost about half of the genuine ones. This is a very cost-effective way for me and I don't have to endanger my health from inhaling toner dust