@Daru’s way of doing it is a great option, and it’s what I’ve been doing as well.
A few other useful ways to go about it:
You could try using Kaniwani with a sheet of paper handy. Kaniwani trains you in the opposite manner from Wanikani - It gives you the definition and you produce the kanji. Instead of just typing them all in, only let yourself count it as correct if you can write it out on paper first.
If digital options are more your style, you can still learn to write out the kanji using this Anki deck. It follows WaniKani and provides you with a space to draw out the kanji. Then, it overlays the proper kanji.
Just be cautious. These options for learning to write kanji all take time. And with wanikani taking 1-3 hours a day at later levels, you may find it difficult to keep up. I’d definitely recommend prioritizing learning Grammar over writing kanji. And, unless your only interest is in purely written communication, I’d also prioritize speaking and listening comprehension practice, whether it be through a class, conversation partner, or audio lessons, over kanji writing.