When the DECT M-SC-Series base station is started, it is usually assigned an IP address by the DHCP server. (Usually a real server, but can also be a Fritzbox.)
To determine the IP address of your DECT M-SC-Series base station, please use a suitable handset (M15 SC).
After you have paired the M15 SC handset with the base, you can navigate to:
Menu -> Status -> Network -> IPv4
How to log into the web interface of a base of the DECT-M-SC series can be found here: Entering Web Interface - WUI of your Snom DECT-M-SC Series Base
If this does not work, here can you find how you can reset your Base to factory settings.