Use a pocket knife to scrape off the broken vane and glue.

Be sure to hold the blade away from you, at a 45 degree angle from the arrow.

Periodically check the arrow, by rubbing your finger on the surface of the arrow, to see if all the glue has been removed.

If all the glue has been removed the arrow will be smooth. If the glue hasn't been removed completely, your finger will feel small raises on the arrow.