Lightroom 6 unregister all computer

The Help Manual tells me the following, but there is no place to contact adobe.

Please unregister all my old computer.

Thank you.

Have you lost access to your previous computer?

If you cannot access the previous computer on which you installed the app—whether it was stolen, was lost, crashed, or locked—you need to contact Adobe to deactivate the app.

If you upgraded your computer’s hardware, replaced a hard drive, upgraded your operating system, or reformatted your computer before deactivating your software, you may have disrupted the activation connection.