The first thing to do is turn on SVG icons in Customize > General.
Then, try this filter:
add_filter( 'generate_svg_icon', function( $output, $icon ) {
if ( 'menu-bars' === $icon ) {
$output = '<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24"><path d="M0 0h24v24H0z" fill="none"/><path d="M3 18h18v-2H3v2zm0-5h18v-2H3v2zm0-7v2h18V6H3z"/></svg>';
}
return $output;
}, 10, 2 );
Let me know 🙂