To control Elgato Key Light via Elgato Stream Deck, you will need to download two things:
• Elgato Stream Deck software version 4.0 or later
• Elgato Control Center software version 1.0 or later
You can get those here:
Then, when you launch Elgato Stream Deck software, go to the Control Center section.
You will find the Elgato Key Light controls there:
• Set Brightness
• Adjust Brightness
• Set Temperature
• Adjust Temperature
Drag those Actions to the left, on the keys you prefer. Setup up each Action according to your needs.