Podcastics do not have a user interface from which to set up a 301 redirect. Therefore, to migrate your feed, you must email the Podcastics support team at firstname.lastname@example.org asking them to set up a 301 redirect from your Podcastics RSS feed to your new RSS.com feed.
Here is an email template that you can use:
Hi Podcastics Support,
I'm moving my podcast to a new host provider and kindly request that you apply a redirect for the following show (Insert Your Podcastics feed Here)
Can you please apply a 301 redirect to my new RSS.com feed at (insert your RSS.com feed here, for example, https://media.rss.com/myRSSfeed/feed.xml)
Please let me know if you need any more information
Thanks in advance.