Ellabee -- I don't have any online recipes for you at all, is there a chance you were referring to editing a personal recipe? If so, it is basically the same procedure Jane described -- clicking the pencil icon next to the title/author, then making and saving any necessary changes. For personal recipes, the pencil icon is visible on your bookshelf/search results as well as on the specific recipe's details page.
Also, I do proofread all the new online recipes members add, so if you realize you've missed an ingredient after you've submitted the recipe, chances are I will have already seen it and fixed it before it shows up on your bookshelf.