This Seeking Tech video guide will show you how to complete the Monsieur Frappe side quest in the Verso’s Drafts location of Clair Obscur: Expedition 33.
To beat him, you need to parry his attacks three times. Press the parry button anytime you think he is about to attack. Even if he doesn’t should be able to recover in time to parry.
If you are having issues, try lowering the difficulty mode to increase your parry window.
You can find the video walkthrough below: