MLA

Kissinger, Henry, 1923-2023. Yost, Charles. Box 303, folder 14. 1968, undated. https://collections.library.yale.edu/catalog/11774546.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 303, folder 14"])(1968, undated)[Yost, Charles]. https://collections.library.yale.edu/catalog/11774546.