You need to register in the instance you want and then add the new account to the app

There will likely eventually be a way to migrate your account just like mastodon, however kbin is a different platform altogether and you would need a new account there.

Nope, so far the app will log into the last account you’ve used.

The default instance is your instance (local). In the setting you can change this to all. Under user settings.

So can I log into Jerboa with my kbin.social account or not?
Edit: Turns out I can’t. Jerboa seems pretty useless to me if I can’t filter out the unwanted instances.