Sitename not showing up in Attitude Theme

My titles and meta have Force rewrite selected. My post types have %%title%% %%page%% %%sep%% %%sitename%% selected. Your website provides a solution in case the sitename doesn’t show up but I am using Attitude theme and it is built on hooks. I don’t know how to modify the header.php so the sitename automatically shows up in the snippet. Can you kindly help?

https://www.ads-software.com/extend/plugins/wordpress-seo/