Insert a 'Next page' Section break at the end of the 'Executive Summary', then access the header in the following page and unlink it from the previous Section's header. You can move one copy of your textbox into the header of the document's first page, as well as delete the other copies of that textbox.
This is no more than intermediate-level Word document construction. For lots of useful information, see:
http://wordfaqs.ssbarnhill.com/articles.htm
http://wordfaqs.ssbarnhill.com/tutorials.htm
http://addbalance.com/usersguide/index.htm
https://gregmaxey.com/word_tips.html
http://www.gmayor.com/word_pages.htm