For your offline Nest Protect, have you tried these steps? What happened?
If you deleted a Nest Protect from the app, you'll need to reset it to be able to add it back to the app:
hi...I had to remove each NEST protect from my app (I have three of them in my house) and then I was able to reset them all using the new WiFi. You have to scan the barcode in the back of each device when you are resetting them. Hope this helps.
I wanted to check in and see if you are still in need of any help with your device. Please let me know, as I would be happy to assist, and answer any questions you may have.
We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.