Can you get the controller into the state where quadrant 2 is blinking yellow? See
https://support.rachio.com/hc/en-us/articles/360003815533-Light-Codes-Rachio-3-
If not, factory reset the controller and try again.
Once quadrant 2 is blinking yellow, go to your phone’s Wi-Fi settings (without running the app) and look for a network name starting with Rachio e.g. Rachio-1A2B3C. If you can see this network and have a Mac, Windows or Linux computer with Wi-Fi, use that to ‘provision’ the controller as described in this post:
If that fails, post details of where it went wrong. If it “succeeds” but the controller is still offline, post what you know about the connection e.g. does it show as a device in your router? Can you ping it?