Thanks for your interest in the NRATV add-on.
Click this
link to my repository and download the zip file to your computer.
For a newer Shield, put the repository zip file on a USB thumb drive or USB HDD. Plug in the USB thumb drive or HDD into the Shield.
For an older Shield, use a microSD card. So same thing, with microSD card reader connected to your computer, put the repository zip on microSD, then put microSd into Shield.
Next you would run Kodi on the Shield. Click on Addons > Download > .. > Install from zip file
Then you have to navigate the repository zip file on the USB device (or microSD), select it and click OK. Then you "Install from repository", select my repo, video add-ons and select NRATV. Hey you might like Best of NHK add-on as well, so give it a try.
Hope this was helpful.