understanding from private addresses
Reserved Ranges:
Specific ranges of IPv4 addresses are reserved by the Internet Assigned Numbers Authority (IANA) for private use, including:
A -10.0.0.0 to 10.255.255.255
B – 172.16.0.0 to 172.31.255.255
C- 192.168.0.0 to 192.168.255.255
So if you uses theses private address with the https part you should be able to access the router login, but if the firmware was only coded to use Class C ONLY then I assume that would be the problem.