Installing a filter

Hello,

I want to install this recommended filter to speed up my website:

add_filter( 'generate_fontawesome_essentials', 'tu_fontawesome_essentials' );
function tu_fontawesome_essentials() {
return true;
}

But I can´t follow these instructions:

https://docs.generatepress.com/article/adding-php/

When somebody can tell me, on which file i should add this code, i could add it easily with php.

Sorry for my bad english!