Allow Shop Managers to add another role user - using Import Export WordPress Users and WooCommerce Customers plugin by WebToffee

functions.php

<?php

/**
 * Allow Shop Managers to add another shop manager/custom role
 */
function wt_shop_manager_role_edit_capabilities($roles) {

    $roles[] = 'shop_manager'; // change role here for custom roles
    $roles[] = 'customrole'; // change role here for custom roles
    return $roles;
}

add_filter('woocommerce_shop_manager_editable_roles', 'wt_shop_manager_role_edit_capabilities');