Thanks all. It looks like I have painted myself in to a corner here!
My Ipad Mini tells me it is currently running iOS 9.3.6 and my "software is up to date".
The internet tells me that the original ipad mini can't run iOS 10.
I guess I must have been running a legacy version of SkyDemon which is no longer available from the App Store.
Ho hum. Serves me right for fiddling!