Look and listen to the Requiem Mass by Mozart once again. This is the movement called Confutatis Maledictis, and this example comes just two bars before the second plea: “Voca Me”.
Here is the score:
A small clue for you: The key of the waltz is E♭ major. Go through the creative steps. i) The submediant is C. ii) The flattened submediant therefore is C♭. iii) So, look for a C♭ in the left hand. iv) Then, try and analyse onto which chord it resolves.