MLA

Kissinger, Henry, 1923-2023. Armstrong, Hamilton Fish. Box 2, folder 20. 1967-1968, undated. https://collections.library.yale.edu/catalog/11782319.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 2, folder 20"])(1967-1968, undated)[Armstrong, Hamilton Fish]. https://collections.library.yale.edu/catalog/11782319.