[Notification Options] Can no longer access files as an option for ringtone

[ConnDublin]

When I was working initially in K9 > Setting > Account Setting > Notifications it asked if I wanted inbuilt options or to use File Manager. By accident, I hit Always when selecting inbuilt options and I can no longer get back to a choice for File Manager.

Anybody know how to reset this, short of uninstalling and re-installing the entire App? Any and all help much appreciated! Using version 5.004 on Lollipop