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On a Mac just start Terminal (Applications > Utilities) and type

defaults write com.apple.iTunes carrier-testing -bool TRUE

Restart iTunes if you had it open

In Windows:

Press Windows Key + R to open the run dialog. Enter in cmd then click OK

Step 3: Enter the following command into the Command Prompt window.

"C:\Program Files\iTunes\iTunes.exe" /setPrefInt carrier-testing 1

Restart iTunes if open.
 
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