I'm surprised this hasn't been mentioned yet - just have fun.
Honestly, when I was grinding out K2's boss rush (or any hard segment, really), I enjoy talking to my chat about non-related things and just having a good time. Whether it's memes, food talk, or something else, it's always fun to just casually get your mind off of the grind at-hand while you slowly develop muscle memory. Eventually, you'll beat it without even realizing you improved at all!