If you have a perpetual (node-locked) license and forgot to deactivate your license on your previous machine, please perform the following steps in order to activate your current license on your new machine.
Open the redshift licensing tool:
It should look something like this and it was installed automatically at the same time when you installed Redshift.
If you can't find it you will also be able to locate it here as well:
Mac; in the Application s- Redshift Folder
Inside that tool click 'Activate License'
It may then note that your license is still used in another machine.
It should then offer you the opportunity to 'reset' your license.
(note: you can only do this three times max)
Then you can activate your license again.
If this does not work, please raise a support case at support.maxon.net