How to set the bell? Please note that I am talking about the ringtone that people hear when they call me, not the ringtone that I can hear.

That's a ringtone. You can call customer service or go to the business hall to handle it. The other easiest way is to go to the business hall and ask for the color ring code. When you come back, you can send a text message sz plus a color ring code to 10086. If you want to cancel any CRBT qx plus CRBT code, you can cancel all gbcl and send it to 10086 (sending information to 1086 is free).