스태프 아이콘을 어떻게 변경하나요?

How i can use a custome svg file as Icon
I have uploaded the svg file on the Dark Design.


And i have the following custome header

<script type="text/discourse-plugin" version="0.8">
api.replaceIcon('shield-alt', '$shield-alt-duotone');
</script>

But the Icon is not visible.