How i can change the Staff Icon

[Canapin (Coin-coin le Canapin)]

This it not how it works. $shield-alt-duotone is a variable meant to be used in your custom CSS. The first topic I linked earlier explains how to replace icons with new ones with an SVG file:

Replace Discourse's default SVG icons with custom icons in a theme

As of Discourse 2.3.0.beta6 (and thanks to @pmusaraj) you can now add custom SVG icons and override the defaults within a theme. You can replace a single icon, or the entire set. Here’s how: Create an SVG Spritesheet To get started, you must combine your SVG icons into a single spritesheet. If you have a few icons it’s easy enough to do this manually. If you have many icons, there are ways to automate this. If you’re not already familiar with some of the Grunt tools to combine SVGs, the simple…