remove tabs

Your best bet is to use this function:

add_action('admin_head','generate_custom_admin_head');
function generate_custom_admin_head() {
   ?>
      <style>
         #menu-appearance {display:none;}
      </style>
   <?php
}

That will hide the "Appearance" section of the Dashboard, which includes Customize and GeneratePress.

A more thorough version which you can use with the above is here: https://gist.github.com/generatepress/f04d0881f806e84be0ac

It will fully remove everything GP related - good for white labeling.

These functions can go in your child theme's functions.php file, or in a new plugin (recommended) - use Pluginception to create the plugin super easily.

Thank you.

You're welcome :)