Possible to duplicate header across website?

Site URL: https://www.treeoflifemysteryschool.com/

Hello,

I need to make a change to the header on this website: https://www.treeoflifemysteryschool.com/ but do not want to go into each individual page and manually rewrite/recode the header. 

Is it possible to copy and paste (or somehow use code) to duplicate the header quickly and easily across the site?

This is the new header appearance:

https://www.treeoflifemysteryschool.com/hometest

Thanks!