MLA

Kissinger, Henry, 1923-2023. Kennedy, John. Box 34, folder 19. 1958, undated. https://collections.library.yale.edu/catalog/11782981.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 34, folder 19"])(1958, undated)[Kennedy, John]. https://collections.library.yale.edu/catalog/11782981.