gppro_preview_buttons

By default, there are two buttons to the far right of the live preview. One to refresh the content, the other to clear out any live changes.
Preview Buttons
This filter allows you to add, remove, or modify those buttons.

Adding a custom button

function my_new_preview_button() {

	return '<span class="button button-small button-secondary" title="'.__( 'Some Action', 'my-text-domain' ).'">'.__( 'Some Action', 'my-text-domain' ).'</span>';

}
add_filter( 'gppro_preview_buttons', 'my_new_preview_button' );