You can connect the Smart TV to the DG-HR 3420 only if the TV supports WiFi, since the device you have mentioned is actually a router. Go to the network settings of the SmartTV and look for the network name assigned on the router. Most smart TVs support all types of encryption protocols. Input the password, and the Smart TV should be connected.
After a successfull connection, the SMART TV might require firmware update. Don't be scared and follow the instructions on screen.