If you have already submitted your podcast to iTunes or Apple Podcasts, then you will get a unique iTunes URL. This is a way to link to your show on iTunes or Apple Podcasts.
You can find this URL just by searching iTunes for your show, or by searching Google for your show name + itunes, or by getting it directly from Apple Podcasts Connect.
Here's an example iTunes URL for the show This American Life https://podcasts.apple.com/us/podcast/this-american-life/id201671138
The podcast's iTunes ID is the last numerical part of this URL, that is:
Having problems with Apple Podcasts? Go to the iTunes Podcast page, and at the bottom click the link saying Contact Us.