If you want to use your existing devices, you have 2 options.
(Recommended) Option 1: Set up a new network with Nest Wifi as your primary router and Google Wifi or Nest Wifi point as a network extender
This option means resetting your existing devices, setting up Nest Wifi as the primary router, then adding your Nest Wifi and/or Google Wifi points. This gives you the best possible setup as it means you can take advantage of the improved range and speed of the Nest Wifi router, but it does mean you'll lose your current Wifi network settings and any custom schedules, meaning you would need to configure those again. You won't lose the network name though, you would just need to configure it again.
Option 2: Add Nest Wifi router to an existing Google Wifi network
This option means you'll leave your existing devices as they are, adding your Nest Wifi router and/or points as addons to your existing network. This option doesn't take advantage of the improved range and speed of the Nest Wifi router, but it allows you to keep your current Wifi network settings and custom schedules.
Full details:
Use Nest Wifi and Google Wifi devices on the same network - Google Nest Help
Worth highlighting if you're looking at Nest Wifi Pro, and not Nest Wifi, Nest Wifi Pro can't be combined with Nest Wifi or Google Wifi.
