I’m new to the Dimmer 2 too but did set up a couple last week. Have you tried the full reset (hold down the B button until the LED turns yellow) and starting again from scratch?
DTH is the device handler. I use this one for the Dimmer 2: [RELEASE] Fibaro Dimmer 2 (FGD-212) - Advanced DTH (V2)
The IDE is https://account.smartthings.com - this is where you can manage your devices, smartapps and device handlers.
If this second part is new to you, i’d recommend some more reading before travelling further down the path you’re on. Fibaro 2 for Dummies is a more advanced topic.