How can i set a particular tone for voicemail message? xiaomi 6 note pro

[AndyIreland]

Hello, i am sure I managed to do this on other androids but on my Note 6 Pro with miui10 if I go into 'voicemal' settings i can select the default number to dial for voicemail but i cannot see where I can change the notification tone to one I want. only vibrate 'on or off'
How can I change ringtone for voicemail please?