How do I remove Facebook icon on Apple Watch face?

There’s a notification. Slide a finger down from off the top onto the crystal to view it. Or tap and hold.

Notifications on your Apple Watch - Apple Support

If you don’t want the Facebook app, you can delete the app from the iPhone, or can use the Watch app to remove apps from installing on the Watch.

You have asked us to guess exactly what “appeared” means. Might it be a complication such as a shortcut, for example?

Privide a screenshot, or thoroughly describe “appeared”.

Take a screenshot on Apple Watch - Apple Support

The screenshot helps immensely!

The icon means Facebook is using some feature such as your location. Tap the Facebook icon for additional details. See especially “Check the Status in Control Center” here.

Use Control Center on Apple Watch - Apple Support

have you tried using your phone to delete it

Glad it was helpful. Glad you were able to post the screenshot.

Enjoy your Apple gear.