Downloading a streaming episode on iPad mini

As suggested you'll need to provide more details.

What streaming service or app are you using?

Episode of what exactly?

If available the episode should have a download option under it or in a menu you can access.

For instance on the Apple TV app you can get the download option from the ... menu under the episode art card or by clicking the down arrow at the top right corner of the episodes details page.

Without knowing where or what app you are using to access said episode it's hard to be any more specific.

What streaming service and App are you using?

Both the App and the streaming service will determine how - or even if - you can download the show for offline viewing.