Select the panel called Books, Videos, and More. This will take you to a search box for the library catalog.
Keep the initial search to All (if you select music it will limit to recorded music). Type in a composer, song name, piece title, or any other keywords related to the score you are looking for. Then press enter to create your search results.
Pro-Tip: Put any phrase longer than a single word in quotation marks, like "Resurrection Symphony."
Once you have a list of search results, use the filter for musical scores located under the format header.