I'm not sure the setup of your modem or the IP's but it is likely that it could be that address.
It's usually one of these:
192.168.0.1
192.168.2.1
192.169.0.1
192.169.2.1
Try typing them into your web browser and see if one of them load to a page.
You would need to know the login and password of the modem as well, If one was not set by you, family, or your ISP then it is likely default, which would also mean it could be different depending on your modems brand.
Some default to having the username admin, and having no password.