You can not edit the online styles, unless you have an administrator for you Endnote at your institution (but I have never figured out how that works, Tech support may know).
The best you could do is to try to find a superscript style. Are you needing a footnote style, or when you are ready to submit, download a desktop trial copy and edit the output style to get what you need. – 1,2,3 is unusual. usually it would be 1-3.