To reset the Nest Guard, you have to do the following. I just did this recently.
1) Go on to the Nest app and delete the Guard by going into Settings, Click on the Guard, and then Remove Device.
2) Go back to the Nest Guard and hold down the '2' button for about 10 seconds. The voice prompt will first list the version and then instruct you when to remove your finger to allow a complete system reset.
3) Once the Nest Guard reboots, you can now add it back to the Nest App as a new device. You can then add all your other devices next.
Hope this helps...
I apologize for my late response and thank you for all of your patience while waiting for a reply. I understand how frustrating your situation must be, and I would love to help however I can. Here is an article that goes over changing settings for your Nest Tag. I hope that information helps!