how to activate AMP transitional mode: basic question

Hello,

I recently installed AMP for WordPress plugin.
My website is not geared toward mobile users, but as Google moved on to mobile indexing, Google is not indexing my site siting multiple issues.

So I installed AMP for WordPress and chose “Transitional Mode (formerly Paired).”
According to the support document, “The transitional mode can be enabled either via the admin screen, or you programmatically via:

add_theme_support( ‘amp’, array(
‘paired’ => true,
) );

This is my truly basic question. WHERE DO I GO to add this code? Does “Admin screen” mean WP dashboard? Where do I go from there? Or do I go to my server cPanel? It’s greatly appreciated if you could just let me know exactly where I copy/paste it. Thanks!

The page I need help with: [log in to see the link]