I downloadeded it on the Firestick itself via the search function. My app version is, I believe, 6.4.13. I will double check this for you when home this evening.
The strange thing is that the app version was the same for both the UK version that I was erroneously using and the Irish version. The reason I knew it was actually different was that it had fewer reviews and a better rating on the app store than the app I had previously installed.
By the way, make sure to give your Firestick some time to sync with your Amazon account before searching for the new app. I had to do 2 restarts over a 15 minute period to see the new app show up.
@MJSG27Okay I finally figured this out. The app on my LG tv is 6.4.13 and is working but on the firestick was 2.19.0.
I couldn't find the 6.4.13 version anywhere. But I eventually realised there are two versions on the app store that are both 2.19.0 but only one will be downloadable depending on you location preferences.
Change the region to Ireland.
Sign into the Amazon account associated with your Firestick.
Hover over Accounts and Lists and select Your content and devices.