How to setup Google Analytics Form Submission Goals in SiteCore

My website is built on Sitecore CMS.

We have a /contact-us/ page where a form is provided for users. Once the click on Submit button, the same page loads with a submission confirmation message.

I want to setup goals on how many times successful submissions are done.

So how to configure conversion goals?

I think I can use "event" from Google Tag Manager.. but not sure how to find a page-id or form-id in SiteCore.