Thanks for your reply.
I can't get "Change Folder" to appear, either in Mail, or via Data File then Mail.
So I exited Outlook, removed my profile, then deleted all the PST files in 3 folders on C: (there was only ever 1 pst on my old 32-bit PC), then ran Control Panel, MS-Office Repair, restored backup of my pst, reloaded Outlook, entered new profile, and opened (not imported) my old pst.
Then checked for "Change Folder" but not there.