You can replace the default launcher icon with a custom image (PNG or GIF) when using the Float launcher type. Here's how:
Go to Dashboard → Settings → Widget and open the widget you want to customize.
In the Launcher Settings section, make sure the Type is set to Float.
Under Float Icon, select Custom Icon from the dropdown.
Click the upload area that appears and upload your icon file (PNG or GIF, any reasonable size).
Save your widget settings. Your custom icon will now appear as the launcher button on your site.
Note: The custom icon option is only available for the Float launcher type. If your widget uses Badge, Drawer, or Line mode, you will not see the custom icon upload option.