The easiest way is probably to use “the big switch” smart app. It’s available from the “more” section of the smart set up in the official mobile app.
There are a number of other smart apps that will also do this, such as “dim with me” and “dim and dimmer” they all offer slightly different features.
See the “community created smart apps” section of the forum for more of these:
https://community.smartthings.com/c/projects-stories/created-smart-apps