There is no plug on the converter to drain it. You can try getting the trans flushed to get the coolant out of the trans, but don't be surprised if you have problems. I've seen coolant make the clutch material flake off the clutch packs. To fix it completely you should rebuild the trans and replace the converter. If it was mine, I'd flush the trans, and then inspect the trans pan for flakes of clutch material in a few hundred miles or so. Don't find any flakes and you probably good to go.
Good luck,
Joe