What do I do if the Intuvia 100 displays a countdown, a 12-character code and barcode?

The 12-character code is the MAC address. It connects your Intuvia 100 to the smart system. You can find instructions on how to connect here.
If your Intuvia 100 is already connected to the smart system, you don't need to do anything. Wait for the 30-second countdown to finish and use your Intuvia 100 as usual.