MLA

Kissinger, Henry, 1923-2023. Mitchell, Donald. Box 42, folder 7. 1958. https://collections.library.yale.edu/catalog/11783152.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 42, folder 7"])(1958)[Mitchell, Donald]. https://collections.library.yale.edu/catalog/11783152.