Haven't used Ruby so I can't speak to the correct syntax, but for the Appium driver it looks like slipy12 already gave you the correct answer to use elements (plural) to get a list of all elements that match.
In general it's always helpful if you provide your page XML for us to look at. You may not even have the id correct for your element which would cause both element (singular) and elements (plural) to fail to find anything.