Adding /d/domain-name-goes-here to kbin's normal web address will take you to that instance's "homepage" and you can block it there. For example, https://kbin.social/d/feddit.de
Keep in mind, this will only block posts coming from that instance, so you'll still be seeing comments from those users elsewhere, but it should take care of a good deal of it on your feed if you don't mind losing out on the three or four communities there that aren't in german
NotTheOnlyGamer