AFAIK there are no tools like that, yet. Keep in mind that Lemmy (and surely Kbin too as I think it's newer) are still very young applications (Lemmy is on version 0.17/18 currently). Development will probably accelerate now as it brought a lot of interest in developers and, as I understand it right now, the github is very active right now.
Mastodon does have migration tools to carry your follows with you, so it's definitely possible and are probably coming soon.