Admob integration in Xcode

I'm completely new to xcode, and am trying to test ads on the hello world unity project that Google gives. I'm getting this message in the console after running:

<Google> To get test ads on this device, set: GADMobileAds.sharedInstance.requestConfiguration.testDeviceIdentifiers = @[ @"4872816d81391b834dae20c53a9efca8" ];

But have no idea actually where to do such a thing. Please could someone advise me on where I should be calling this? Thanks in advance

For testing you would use this AdUnit ID ca-app-pub-3940256099942544/2435281174

Admob integration in Xcode
 
 
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