How to add code to a specific spot

We’d like to add a snippet of code for “AddThis”. Here is our page:

https://www.ncmassageconnection.org

We’d like the AddThis icons to display on each page in the very upper right corner where you see a white area that is perfect for this. The upper right corner across from where it says “North Cascade Massage Connection” in black text.

Not sure where to put the code — is this part of the header.php file?

Thanks!