Web citations

I need to cite in ACP style, how can I create a new/add a citation style to Endnote web?

I don’t believe you can, unless you have Endnote Web version thru an institution that subscribes to Web of Science and then the institution’s administrator is supposed to have the ability.  This is a desktop feature.   There are only 21 styles in the basic version of Endnote online that is free.