A family of Microsoft word processing software products for creating web, email, and print documents.
Word can't do what you're asking by using the Columns feature. You can insert a two-column table and use it that way. This is discussed in http://www.word.mvps.org/FAQs/Formatting/UsingColumns.htm. (Although the pictures there are from Word 2003, the features work the same way in all later versions.)
If you insert a section break before the endnotes, you can select three columns for that section.