After hours forward to mobile, how to update mobile #

[syadnom]

I've created a call flow so I can map it to a BLF that enables/disables night mode. When in night mode, I want calls to be sent to a cell phone but I'd like end users to be able to update this number by dialing something on the phone.

Can someone point me the right way?

I'm open to an IVR or feature code etc etc.

Thanks