You need to cast your screen from a Chrome browser, how that integrates or doesn't with apple stuffs, I'm content to say I've no idea.
If your tv is already set up to cast from a mobile device, you just need the stream to play through the Chrome browser on it, to cast it.
click "cast", select from the drop down menu "desktop", then select the device you want to cast to if you have more than one ie...living room TV.
That's it.

Sorted it with an app on my iPad.

Well impressed with Trinity TV, excellent value.

I noticed there's a 'downloads' button on the Trinity TV dashboard. Can the videos be downloaded? If so, how?

It's Apple play and it's free Although your tv has to be compatible with it, but there maybe a download for your TV to allow that.
Also if you have a smart TV and it's connected to the internet via a WiFi or RJ45 connection, then just go to the web porthole and open trinity tv from there

I bought a years subscription last week and all i had to do was hit smart view on my phone and it sends it too my smart tv from my phone

I watch it using the Silk internet App on my firestick on my TV or directly on my mac. You do need a good Wifi signal though and it struggles at 720 but watchable at 540.