If you are referring to customizing your characters after creation, there is no way to customize characters past their creation, and you'd need to delete a character to change its appearance. Looking at your account, I'm seeing that you played Destiny 1, and had characters during that game. Since you played before August 1st, your character's appearance from the first game transferred over to the second game, so any characters in Destiny 2 would look identical to their Destiny 1 counterpart. You'd need to delete that character in Destiny 2 to make any appearance changes.