Set role after checkout for WooCommerce

set-custom-role-after-checkout.php

<?php
/**
 * Set the default role to employer after checkout.
 *
 * @param int $order_id
 * @return void
 */
function marce_set_employer_role_after_checkout( $order_id ) {
    $order = new WC_Order( $order_id );
    $user  = $order->get_user();

    if( false !== $user && ! user_can( $user, 'administrator' ) ){
        $role = 'employer';
        $user->set_role( $role );  
    }  
}
add_action( 'woocommerce_thankyou', 'marce_set_employer_role_after_checkout', 100, 1 );