@Bronnybee
Google Nest does not make it easy to change Wi-Fi settings; that's why their first recommendation is to set the network name (SSID) and password on your new router/modem to the same values used on your old router modem.
If you can't do that, then you need to perform a factory reset on your Google Home:
https://support.google.com/googlenest/answer/10165378?hl=en-AU&sjid=7810138548616974504-NC#zippy=%2C...
I don't know why you are referring to a two-factor authentication message being sent to your old phone number. If you ALSO changed the phone number you're using for two-factor authentication for your Google Account, you should have changed the number on your Google Account before switching phone numbers. If that's your situation, I'm not sure there's a resolution; This is Google Account's Help on changing phone numbers:
https://support.google.com/accounts/answer/3463280
If I've misunderstood what you meant by "my google home was sent my old phone number", my apologies.
