Using the tool to reset your own printer is generally unenforceable for personal use. However, selling the tool or using it in a paid repair service without Canon certification violates their terms of service.
: Canon officially recommends contacting a service center to replace the physical ink absorber pads when they are full, rather than just resetting the software counter. Canon Service Tool V.3900 Download
Press and hold the (red triangle) button, then press and hold Power . Using the tool to reset your own printer