Nighthawk M1 - Data offloading won't work

Before making any changes, can you log into the other router and find out if it's IP address is indeed 192.168.1.1? If this isn't the case, the problem must be something else. If it's the same as the M1, you could try changing the M1 IP to 192.168.1.2, assuming that's not included in the DHCP address range of the other router, in which case you could still have an IP address clash. Remember that if you change the M1 IP address, you'll have to use that new address if you want to access its interface via a browser. If this doesn't work out, you can always do a factory reset on the M1 to get the default gateway IP address back - you'll of course lose any other setting changes from default that you've made.