MLA

Kissinger, Henry, 1923-2023. Clapp, Mary. Box 13, folder 3. 1967 May-June. https://collections.library.yale.edu/catalog/11782511.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 13, folder 3"])(1967 May-June)[Clapp, Mary]. https://collections.library.yale.edu/catalog/11782511.