Gently remove the cone. Unsolder lead-in wires first. Obtain a piece of dowelling that fits snugly inside of the voice coil form. Take the windings and carefully put them back into place. Massage a little Elmer's glue into the windings, or use something stronger if you wish. Make sure you put the windings in place well, first, before you permanently glue them into place. Be sure that the glue is smooth on the surface so that it doesn't rub the pole piece. However, don't skimp with the glue. Make sure that the bonding is strong. The wire should be thoroughly covered in glue. You can also use varnish, which is fairly strong. It takes a while to dry, though.
Thomas