Excellent! Thank you.
Posting to help others in the future
add_filter( 'asp_fontend_get_taxonomy_terms', 'asp_reorder_terms', 1, 3 );
function asp_reorder_terms($terms, $taxonomy, $args) {
if ( $taxonomy == 'product_tag' ) {//'product_tag' is for WooCommerce
$custom_order = [ 'slug2' , 'slug3' , 'slug4' , 'slug1' ];//desired order of terms using their slug
$terms_reordered = [];
$i = 0;
foreach($custom_order as $slug => $data){
foreach($terms as $term){
if($term->slug == $slug){
$terms_reordered[$i] = $term;
unset($term);//unset so mark it reordered
}
}
$i++;
}
return array_merge($terms_reordered, $terms);//merge in any terms not reordered
}
return $terms;
}