I hope you have developed a custom payment extension. You can change the action by modifying the following file in your module.
app/code/<Vendor>/<Module>/view/frontend/web/js/view/payment/method-renderer/<component>.js
define(
[ 'jquery',
'Magento_Checkout/js/view/payment/default',
'mage/url'
],
function ($, Component, url) {
'use strict';
return Component.extend(
{
defaults: {
template: '<Vendor_Module>/payment/<template>',
redirectAfterPlaceOrder: false
},
placeOrder: function () {
//overriding placeOrder function
window.location.replace(url.build('module/new/URL'));
}
afterPlaceOrder: function () {
//redirecting after placing order in Magento
window.location.replace(url.build('module/new/URL'));
}
}
);
});