Endnote numbers citations/bibliography according to the output style you choose. That would be usually alphabetically or by appearance. So what is your prefered sort order and what is the output style you are using? Options are altered by editing the Sort of the Bibliography (see capture.jpg for settings options)
Or, is this within a grouped citation. Usually a grouped citation follows the same rules as the bibliography, but you can adjust that but it applies to all groups. (see capture2.jpg for settings options). If a group and you have chosen by appearance and “don’t sort” and you want to rearrange them, this is best done from the right click, edit citation, more and then adjust them in that list.
Then save the output style to a new name, and change the output style in use to that new name. You will probably have to “select another style” IN WORD, from the endnote ribbon, the first time, to choose the new style from the full list.