page locations?

What you are looking for is not stored as a file. What you are looking for must be integrated into the template that outputs the page. There are many ways to do this, but none of them leads to Filezilla / FTP.

My recommendation would be to use a plugin which integrates the necessary code for you. As far as I know, this can be done with the official plugin from Google: https://wordpress.org/plugins/google-site-kit/

Alternatively, you can also use one of the many other Google Tag Manager plugins: https://wordpress.org/plugins/tags/google-tag-manager/

And you also have the option of inserting it with individual programming.