How to set the ringtone of BBK landline?

The setting method of BBK landline ringing is as follows: \x0d\ 1. In standby mode, press and hold the flashing/ringing key. \x0d\2。 When the words "song xx" or "ringtone" appear on the display screen, release it, and then press the flashing/ringtone key continuously to select the favorite ringtone. \x0d\3. When the bell is selected or there is no external power supply, the external bell will only ring the ordinary bell. When selecting the ringtone, if you want to terminate the ringtone, just hang up once.