I can understand where finding the good from a bad experience can be challenging. Maybe try looking at it a little differently. Instead of trying to find the good where it didn't exist, look at ways that the experience could have been better. But don't express it as a negative view of the experience. Maybe supplement those thoughts by doing some research.

For example, you could say, "I learned that strong managerial skills and organizational skills are very important in keeping a mental health team working together to help their patients get the best outcome."

It doesn't matter that you didn't see that during your externship, it only matters that it makes sense.

Good luck!