Changing router information due to new modem

I'm writing this as my cable provider suggested that I ask how to update.  I have 1 modems, one for work, one for home.  My router was hooked up to my home modem but after a power outage, the surge fried my previous modem.  I received a new modem and when I hooked it up, it would not recognize the router, or vice/versa.  He said that it was because the old modem had a 4 character address, whereas the new modem has 6+ and the router is still looking for a 4 character.  Is there any way on the modem page to update this, so it finds my modem?