Q.When is best time, and how do I trim rhododendrons?
I have a rhododendron that is 30+ years old. It has always been allowed to grow freestyle, but last year my nephew decided to “surprise” me by trimming it for me. Since then, it has looked so bad, I thought he had killed it. I am trying to nurse it back to its former glory, but dont know when is best time to trim, or how to trim

Certified GKH Gardening Expert
Since your nephew gave it a good trim, you might want to go lightly on the trimming for a while, possibly only to remove spent flowers in the spring.
Here is information on how and when to prune rhododendrons.
https://www.gardeningknowhow.com/ornamental/shrubs/rhododendron/pruning-rhododendrons.htm