Go to the very beginning of the movie where obi-wan and anakin are in space combat over Courescant. Watch the part where all the buzz driods ( the little robots that were all over obi-wans ship) are attacking. Anakin attempts to help by blasting at them and accidently takes off part of obi wans left wing.

Now watch the part after all the buzz driods are gone and the two are about to land in Grievious's ship. Obi's wing is fixed!