Alert notification sound change on Iphone

Hi. I have just installed the camera and it is working fine. The issue I have is how do I change the movement detected notification alert sound on an Iphone (not the siren sound). The default one is very annoying. All I can find is a sound on/off setting not change to my own choice of notification sound. 

I have found I can change it on an android phone (settings/notifications/most recent/security/notification type). 

Thanks in advance

Patrick