If the overwatering is already evident in the leaves all you can do is just put the plant out in the sun and water them less often - but do not stop watering them altogether as then the newer leaves will be dead.
if you are worried that the crape myrtles are dead, simply scrape the bark a little with your fingernails and see if there is some green peeking out. If so, they're still alive. A little overwatering in a week should not cause permanent damage at all. So relax!
How is the soil now? Is it still very clogged after the overwatering? If so, then just dig it up a little and allow it to drain. You could also add some dry soil/compost to compensate. if you have a pot sure the excess water drains off the crape myrtles.
water your crape myrtle tree 1-5times eachweek depending on time year the tree was planted the type of soil being utilized. lightgreen leaves can be sign of over watering while dropping leaves can be sign over watering, while drooping leaves can be a sign of both or under watering.