If you are not able to activate the redirect feature inside your current podcast hosting you have to manually change your podcast feed URL in Google podcast setting up you new RSS.com podcast feed.
1. Access Google Podcast Manager
2. Claim your podcast feed if you did not do yet
3. Click over "Settings" > "Feeds" on the show home page in Google Podcast manager
4. Click "Change Served feed"
5. Add you new RSS.com podcast feed URL