If you have a valid code, the process to unlock the software is straightforward:
Ensure you have the latest compatible version installed on your PC or Mac.
Plug in your iPhone, iPad, or iPod and click "Connect" in the app.
It is common for users to lose their codes over time. If you purchased a license but cannot find your details:
Activation codes starting with TP11 (Windows) or TM11 (Mac) were specifically issued for version 11.