Nest thermostat adding a second phone to control it

[Grahamp]

At time of set up I was able to control my Nest thermostat from both an iPhone and an iPad. Control has now been lost from my iPhone 13 (running latest updates) and I would like to know how to restore that access. 
The app display on my phone shows that I am logged in to the nest account by displaying the installation name and I can view account details. Beneath that it says ‘add product’ but this ends up requiring a network key from the thermostat menu that simply says ‘already installed’ and won’t provide one. 
it is not a wi-fi issue and I have restarted the thermostat. 
Help please. 
Thanks,

Graham

[Markjosephp]

Hello Grahamp,

I'm sorry to hear that you've lost access to your Nest thermostat from the Nest App. I'd be happy to take a look into this for you.

It's most likely that you're signed in to a different account, which doesn't show your thermostat. Ensure that you are logged in with your correct email address, and if you are, check for other available structures where your thermostat might be connected. Check out this guide about switching home structures.

Let me know if that helps.

Best regards,

Mark

[EdwardT]

Hi Grahamp,

I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.
 

Thanks,

Edward

[EdwardT]

Hi Grahamp,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward