Click Settings > Sound, then click the setting item under the Ringtone and Vibration area, set the ringtone for card 1 or card 2, and click Music in the upper right corner of the page to choose your favorite music.

You can also find this music in the "Audio" folder of file management, long press the music file, and click "More - Set as - SIM 1/SIM 2 call ringtone" in the lower right corner.