PowerPack 2.40.1 introduced two filter hooks to change the toggle search icon for both full-screen and minimal styles:

• pp_search_form_toggle_icon_html
• pp_search_form_input_icon_html

To replace the toggle icon with SVG, please add the below code to your current theme’s functions.php file:

add_filter( 'pp_search_form_toggle_icon_html', 'update_search_form_toggle_icon', 10, 2 );
add_filter( 'pp_search_form_input_icon_html', 'update_search_form_toggle_icon', 10, 2 );
function update_pp_search_form_toggle_icon( $icon, $settings ) {
   return '<svg xmlns="http://www.w3.org/2000/svg"  viewBox="0 0 30 30" width="30px" height="30px"><path d="M 13 3 C 7.4889971 3 3 7.4889971 3 13 C 3 18.511003 7.4889971 23 13 23 C 15.396508 23 17.597385 22.148986 19.322266 20.736328 L 25.292969 26.707031 A 1.0001 1.0001 0 1 0 26.707031 25.292969 L 20.736328 19.322266 C 22.148986 17.597385 23 15.396508 23 13 C 23 7.4889971 18.511003 3 13 3 z M 13 5 C 17.430123 5 21 8.5698774 21 13 C 21 17.430123 17.430123 21 13 21 C 8.5698774 21 5 17.430123 5 13 C 5 8.5698774 8.5698774 5 13 5 z"/></svg>';
}

You can replace the SVG code with your custom SVG code if required.