expression, ichidan verb
pull oneself together; get one's act together; brace oneself
Idiomatic expression literally meaning 'to tighten the hoop (of a barrel)', used figuratively to mean regaining self-discipline, focus, or composure after a lapse.
試験が近いから、箍を締めて勉強しなきゃ。
The exam is coming up, so I have to pull myself together and study.
彼は失敗続きだったが、箍を締めて再挑戦した。
He had a string of failures, but he braced himself and tried again.