gateway wifi modem?

This may help:

http://www.routeripaddress.com/routers_with_default_address_10.0.0.138/

Yours could be one made by a manufacturer liste don the page but with a different branding, so these may well be worth trying.

Of course, it'll all come to nowt if the person who initially set the router up has not been so stupid as to leave the default password in place :-)

If you DO get in, consider changing the default password and login and making a note on a sticky label underneath the router, rather than trust to memory.

Twinkerny
September 2017