The song contents of score collections or larger works are not always fully indexed in Novanet. You might have to try more than one search strategy before you find the text.
Before searching Novanet, use Grove Music Online, the Leid, Art Song, and Choral Texts Archive, or another reference source to find:
Search Novanet for the title of the song or aria
This will retrieve scores for which the title of your song or aria is typed into the contents notes.
Search Novanet for the title of the larger work that contains your song or aria (opera, song cycle, musical, or oratorio)
This will retrieve scores that will contain your song or aria, though the catalog record may not have the song or aria title listed.