Changed computer Opus reverted back to evaluation

You don't need a product token. Those are only used when getting licences from boxed versions or third-party resellers (and similar). Once used, they give you a licence code and certificate like you would get if you buy the program direct from the GPSoftware website. Whichever way you go, you end up with a registration code and certificate file in the end.

The certificate file is what the licence manager needs.

If you've lost it, you can get it again here: https://www.gpsoft.com.au/DScripts/lostcode.asp

Related: Common purchasing, upgrading and licensing questions