Thank you.
I haven't found the repair option yet - sometimes software offers repair in the Add/Remove Programs window. But I could only see Uninstall offered there.
I tried setting file associations manually via the Windows right-click Open With... option, but couldn't get the setting to stick. Windows kept displaying the Open With... dialog in a never ending loop. Not sure why.
Luckily I found an answer in another post on this forum. Just in case it helps someone else: In Delphi IDE Options there is a section listing File Associations. Unticking them all, then ticking them again seems to have fixed the issue. Phew!