Metconv suddenly no longer works. In Options it states that it is activated, and the words additional actions appear when a measurement is selected and right-clicked but nothing happens. i.e., when I right click 72 inches for example, nothing happens. It used to give me that measurement instantly in centimetres.
I have tried an online repair of Office 365 etc., but all to no avail. The file appears nowhere.
Any help would be much appreciated.

I've never used this.
This may help: metconv.dll free download | DLL‑files.com

Thank you, but I'm afraid it didn't help. I installed it properly as instructed.
Within Word the Measurement Converter is shown as being in ......Common Files/Microsoft Shared/Smart Tags/. No such subfolder appears on my computer. Perhaps this is one of those items Microsoft has quietly removed without any notification?!
I do have other ways of converting of course, but as an Additional Action it was useful.
Thank you again for taking the time to comment and advise.
Best wishes