First, you need to have each of the switches using that driver. Go to the device in the ST app, click on the three dots and select the Driver option. If the device is not using that driver, you need to change it. If the Driver menu item is not there, the device is still using a DTH driver and you will need to exclude the device and re-add it.
Next, you need to know the device ID of the other switch that you want to mirror the behavior. There are two ways you can find that. 1) use the SmartThings CLI found here GitHub - SmartThingsCommunity/smartthings-cli: Command-line Interface for the SmartThings APIs. or 2) using @TAustin API Browser SmartThings API Browser+ ... Looking for Testers
Once you have the Device ID of the device that will mirror, go to the device that will be mirrored in the ST app, click on the three dots, and select Settings. Scroll to the bottom and you will find the Association Group 2 (and 3). Put the device ID into Group 2 and that will cause the mirror behavior on that device ID.