noun, noun or participle which takes 'suru', intransitive verb
turning over a new leaf; getting a fresh start; changing one's attitude
A yojijukugo used when someone resolves to change their mindset, habits, or life direction, often after a setback or at a turning point. Can be used as a noun or with する to mean 'make a fresh start'.
失敗をきっかけに心機一転、新しい仕事に挑戦した。
After the failure, he turned over a new leaf and took on a new job.
心機一転して、健康的な生活を始めよう。
Let's make a fresh start and begin a healthy lifestyle.