Im not talking down to you, however I’m sorry, but I do expect you to read links that provide solutions. And I dont believe youve been hassled. My explaining over and over again what has already been explained too many times to count is a waste of my time (to be honest), since the solution already exists and you can read it quicker than I can write it.
Its header.php NOT php header, and IF it exists, its within your theme ‘s directory. Since I do not have access to your site, I can only provide this
https://www.performbettergolf.com/blog/wp-content/themes/perform-better-golf/
Thats the URL to your current theme’s directory. Where is is on your server is prolly (but might NOT be) here:
/public-html/blog/wp-content/themes/perform-better-golf