There are many different custom smart apps that community members have created for exactly this purpose, to have one dimmer follow another. They have slightly different features because typically someone will create one for themselves and then share it with the community.
You can find these on the quick browse list in the community – created wiki on the lighting list in the smart app section. I think trendsetter is the most popular right now, but there are a number of others including “Dim and Dimmer” and “Dim with me.”
Another alternative is to use core, although the set up is more complex for that one. It does give you more options, though.
If you haven’t used custom code before, it’s pretty straightforward. Basically you’re going to copy the author’s code and then paste it into your own account.
