You can use the following link to install the user script: https://github.com/entropyofchaos/NHK-Easy-Practice-With-WaniKani/raw/main/NhkEasyPracticeWithWaniKani.user.js
Alternatively, you can click on the script NhkEasyPracticeWithWaniKani.user.js and then click the Raw button.
Once the script is installed using a script manager like Tampermonkey, you will be prompted to enter your WaniKani API Token when loading NHK News.