Based on the provided information, the key to trimming a chevron mustache involves using beard balm to hold and shape the freshly trimmed mustache after it has been trimmed. The video "The Chevron Mustache | How to Shape Your Mustache" offers a visual guide for the process.
While a detailed, step-by-step guide isn't available in the provided text, the emphasis on shaping and holding the trimmed mustache with beard balm is crucial to achieving the desired chevron look.
