That’s odd. If we’re talking about the Shin wanikani leech training it should show up as a button on your dashboard.
And when clicking is goes…
Then you press the button to open up the Leech trainer.
Now it works much like WK does. Just type the answers.
Unlike the Item inspector the leech value here is preset to 2 (?). So, these are all serious leeches. The Item inspector I usually set to 1.01 to catch those stragglers, but which gives you a much higher number of leeches. But that isn’t much of an issue as the Self-Study Quiz is pretty fast if you go through them (well, unless you have a 200+ leeches, but then you can use the Item Inspector to quiz you on on the current page of leeches and so break them down into chunks for review).
Also, do you have the WaniKani framework installed? Most scripts require it, and perhaps the Leech trainer does too? You need to put it at the top of your scripts list in TamperMonkey. The instructions for this, and link, you can find on the Item Inspector script page.
I guess, updating and refreshing the browser might be in order. Since I haven’t made the script, I don’t really know how to fix any issues. But if you had 0 leeches, it should say 0 not X.