it is:

go to the instance locally, say you wanna sub to https://kbin.social/m/Marvel, you’d want to go to this url: https://lemmy.ml/Marvel@kbin.social, then in there you will find a Subscribe button. Just click that.

If you wanna have an automated way of switching from kbin to lemmy, you can use bookmarklets like this:

https://lemmy.world/post/48909

or this:

https://lemmy.world/post/48816

i won’t guide you on how to use a bookmarklet, so google that if you want. you can do what you want without a bookmarklet by following the instructions in my first paragraph.

Just keep in mind that kbin.social has had to turn on DDoS protection which is breaking federation.

As of right now, kbin.social and lemmy instances aren’t talking to each other and can’t see each others content.