I am trying to replace a wall switch with a dimmable TP-Link Smart Wi-Fi Light Switch but when I got into the double gang box there were two reds, white and ground connected to the switch and all the black wires were connected by wire nut in the back. I had the TP-Link switch installed on a single gang switch and it worked beautifully but it that light isn't dimmable, so it wasn't needed there and I'd like to move it. Any help or advice would be greatly appreciated. Thanks in advance
That's a three way switch.
In these pictures, it appears the red wire coming off the black terminal screw goes to the light, but you should confirm that.