Here you go!
This website is my go to for all things plants and garden.. You should find all the info you need as there are a couple thoughts on trimming and pruning. https://www.gardeningknowhow.com/ornamental/shrubs/rhododendron/pruning-rhododendrons.htm
This article may answer your questions
Right after azaleas and rhododendrons are finished blooming is the best time to do any pruning they may need. These shrubs make blooms that flower on the prior year's wood. So you have to be careful when pruning them since buds for next spring will be made this summer, and you don't want to prune those off.
Cut back the plant to expose the inner branches. Follow the branch down to the last whorl of leaves you want to keep and cut just above those leaves, about 1/4 inch above the topmost leaf in this cluster. Large, overgrown rhododendrons can be cut12-15 inches from the ground when necessary.
You can cut them back almost anytime. However, the best time to cut them back is in the spring right after they flower. If you cut them back at any other time, they won't bloom. They develop next year's buds right after flowing.