Deactivating on old PC, reactivating on new PC but getting a trial version instead

I deactivated Trados Studio 2021 on an old PC in early January as I had upgraded my hardware to a new PC. Everything seemed to work fine until after about 3 weeks later when I started getting messages that my trial version was ending on 1 February - which it did. I was not aware of the fact that I was using a trial version as I own a licence for Studio 2021. How do I activate my proper licence now?

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