I’ve reset twice now since joining WK in 2013. Once from 13 to level 8, and after that from 13 to level 5. I’ve never gone all the way down to level 1, and I don’t think that’s necessary especially since you’ve only been on WK for 18 months.
The way that I picked which levels to reset down to was by using the reorder script.
First tick the “sort levels” box and reorder your reviews in ascending order from level 1 to level 12.
Then start doing reviews first clearing out all of level 1, then all of level 2, and so on until you get to a level where most of the vocabulary and kanji seem unfamiliar. Then I would reset to the level before that. I hope it works for you!
It’s great that you’re not giving up and that you’re willing to get back on the horse! I know I’m just an internet stranger, but I’m proud of you!