Endnote Web - adding a new journal style


I use Endnote Web, and have a plug-in for using WORD on my Mac. I’m writing a paper and want to set a bibliographic style for a specific journal. However there only seem to be about 21 bibliographic styles available on Endnote Web…and these ones are also the same available via my plug-in…

I can’t work out how I add an additional bibliographic style not already included on my standard list of 21. Can I do this using Endnote Web?  I feel as though I’m missing something basic - I know it’s possible, and I see there is a plug-in for the journal concerned that Endnote supply - but when I donwload that onto my hard drive it doesn’t seem to make a difference.

Any advice very gratefully received.