MLA

Koch, Frederick R. (Frederick Robinson). Other correspondents and unidentified. Box 47, folder 945. 1865-74, n.d.. https://collections.library.yale.edu/catalog/12214807.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 47, folder 945"])(1865-74, n.d.)[Other correspondents and unidentified]. https://collections.library.yale.edu/catalog/12214807.