You can buy speaker repair kits to replace the surrounds, try some sort of glue like rubber cement (though may react poorly with some material, have to figure out what glue to use), or send them off to one of the places that rebuilds speakers. It is usually fairly inexpensive.
I would start by pulling the driver to see what the other side looks like and try a bead of glue at the very edge (or back lip, keeping it off the surround as much as possible).