How to change header on one page

I am new to wordpress. I was asked by someone who owns the website to make some changes. The person who set it up in wordpress no longer wants to work on it. I know a little html and css but nothing about php and wordpress. I have been able to make a few changes to the home page but it looks nothing like the rest of the pages which is the blue sky template. I was asked to change the header on one of the pages but when I figured out how to change it, all the pages changed. Is there a way to change the header on just one page? Please and Thank you,