Using 5G requires password

I have been using the ARRIS surfboard modem/router Model SBG7600AC2 in 2.4GHz for awhile and it works great.  When I try to switch to 5G it asks for a different password.  How do I set up a different password for 5G?  The only password I have is the one for the 2.4GHz and I don’t remember how I set that up! Thanks,