The WPS button is the called the Pair button on the Smart Modem. It is located on back of modem below WiFi button. Press for at least 5 seconds to connect WiFi device using WPS or pair a DECT 2.0 phone Handset.
If Signal light is red the only thing you could try is moving modem to a different location. The Signal light only indicates the strength of the 4G backup signal and should not effect the performance of the modem when main link is working.