There is a keyboard icon on the bottom right of your review screen. Click it and it will show you that typing / brings up an IME chart. Hit /. You can now see how to type everything in the IME.
edit: I do think it should be way more obvious/easy to find. I missed it for a while.
One issue I have is that I take for granted that if you type n and then another letter, it will automatically make the n a single n … in MOST cases. An example of where it doesn’t is the word onyomi. I’ll type it fast and hit enter… Turns into oniyomi おにょみ
The double n can take some getting used to, but it really is necessary. There are all sorts of IME shenanigans that can happen if you type ん with just one. Don’t worry, it doesn’t take too much to train yourself to do it.
This caught me out on my first couple of tries too. First place I looked was the FAQ but couldn’t find anything.
On which topic, I found myself tripping up on “人” because the reading told me “にん, じん”, and didn’t specify that the comma meant these are two different readings. This led me to think the reading was にんじん instead of a choice. Would make much more sense to separate the two different readings with a / or put it on a different line. And to make it clear in the Mnemonic section that these are different readings.
Learn Hiragana: Tofugu's Ultimate Guide Tofugu which also owns WK, has a great website full of japanese lessons and resources. If you scroll allllll the way down there’s a section for combination hiragana and how to type/say them.