I would suggest watching the following video which goes over the steps of how to edit a style.
https://www.youtube.com/watch?v=TaMdhZ7I6VU
If you still have trouble after watching the video then Please contact Technical Support directly.
1-800-336-4474 option 4 then 1 or
https://support.clarivate.com/Endnote/s/technicalsupport?language=en_US