Hello,
When you uninstalled Net Express, you were prompted to revoke or retain the license. If you revoked the license, then you should be able to find the revoke key in protrev.txt that was created in the 'bin' folder of the Net Express installation folder. If you retained the license, then you can reinstall Net Express on the same machine to use the retained license without the need to get a new response key to activate the license.
If you revoked the key and cannot find protrev.txt or can no longer access the machine, then you need to contact your local Micro Focus SupportLine.
Regards,