To dishevel is to mess up slightly, the way a breeze might dishevel your carefully combed hair.
This verb is nearly always used to talk about tousling someone's hair or mussing their clothes or bedding. So you might carefully tuck in your sheets and comforter only to watch your puppy jump on the bed and dishevel them. Or you might reach over and dishevel your little brother's curls when he's looking particularly adorable. The adjective disheveled came first, from the Old French descheveler, "disarrange the hair."