CaracoleBundle/Resources/assets/app/admin/switchmerchant/switchmerchant.js

$(document).ready(function() {
    initSwitchMerchant() ;
}) ;

function initSwitchMerchant() {
    let $form = $('.nav-switch-merchant form.switch-merchant') ;
    $form.find('select').change(function() {
        $form.submit() ;
    }) ;
}