MLA

Koch, Frederick R. (Frederick Robinson). Music/Phantasietanz. Box 343, folder 2020. n.d.. https://collections.library.yale.edu/catalog/2043667.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 343, folder 2020"])(n.d.)[Music/Phantasietanz]. https://collections.library.yale.edu/catalog/2043667.