Unzip the file you downloaded. It contains a meshy-godot-plugin folder.
If your project has no addons folder, in the Godot FileSystem dock, right-click res://, and then click Create New > Folder.
Enter addons as the folder name.
Click OK.
Drag the meshy-godot-plugin folder into the addons folder in the FileSystem dock. Keep the folder name as it is, because the plugin loads its files from res://addons/meshy-godot-plugin.
In the Godot menu bar, click Project > Project Settings, and then click the Plugins tab.
Select the Enabled checkbox for Meshy official plugin.
When the plugin is enabled, a Meshy tab appears at the top of the editor, next to AssetLib. It opens the panel you use to receive models.