In order to request an Offline Evaluation License, you will need two computers:
1. One computer without internet connection and
2. one that does have internet connection.
Step by step:
In the computer where you don't have internet connection, start the tool and don't close it until the end.
Meanwhile access the computer that does have internet connection and request the offline evaluation license there.
Now go back to the computer without internet connection and check if the "SQLTest" directory has already been created in your "Documents". It might take a few minutes until the SQLTestInstanceKey.txt file shows there.
Once it shows, copy its content into the text box in your internet-connected computer. Now, the license key will be created. (Scroll all the way down to see it or find it in your email inbox in case you checked the box "send by email" while requesting.)
As a final step, download the license key and copy it back into the SQLTest file in your computer that has no internet connection (and the tool still open).
It is important that you copy and save the license key file under the exact same name as it was downloaded in your internet-connected computer, which is SQLTestOfflineEvaluationLicenseKey.txt. Only with this name the tool can fetch the key and incorporate it. It is also very important that the tool is never closed during the entire process.
Now the license status in the tool (left bottom) will change from "Unlicensed" to "Offline Evaluation License".