If PHP is available on your web hosting plan, use PHP Server-Side-Includes for your site wide navigation.
Alt-Web Design & Publishing: Server-Side Includes with PHP
Basically, 1 include file contains only the relevant HTML menu code & nothing more. It's not a complete document, it's a code fragment. Depending on your Bootstrap menu, you will copy & paste just the navbar code into a new file and name it navbar.html or navbar.ssi or whatever you like.
The parent pages in which the include statement occurs will need to be renamed with a .php extension. Most shared web hosts do not parse PHP code in ordinary .html files. If unsure, check with your hosting provider.
Nancy