You can use manual activation to activate products when your computer doesn't have an internet connection or your internet connection does not allow SOAP requests.
You'll need access to another computer with an internet connection and then transfer the installer over on a flash drive.
You can then manually activate the license - here's some step-by-step instructions.
NB: Make sure you leave the original window with the request text open whilst you generate the response text, then paste in the response.
The 'Check for updates' feature from within the software won't work when you're offline. Instead, you can check the Redgate website for updates on a machine with connectivity here to see if you're on the latest version. You can download and transfer updates to your offline machine manually using a USB stick.