Transferring Golem (GNT) from JAXX Wallet

I had some Golem in a Jaxx wallet on my old PC which I no longer have access to. Before losing access I did back up my private key (or at least, I think/hope I did).

My Golem is still in GNT form and I never migrated it to GLM. I have what I believe is the private key but I can't figure out what to do with it. I tried putting it into MyEtherWallet but it says its not a real key? Not sure if this is because it's still in GNT form and not the new GLM form. Any help would be appreciated. It's not worth much (<$50) but if you can help out I'd gladly tip!

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