Redemption is an abstract concept exactly the same as worthiness. Redemption is not always about doing something or atonement, it can be about being saved, reclaiming or being freed from sin.
Plus, as I have pointed out many times it is simplifying the situation to suggest it is ‘all just mental’. It is paradigmatic and within that new paradigm, objective. Thor knows it isn’t just how he thinks of himself that counts. He can’t just pretend he never knew the intrinsic unworthy nature of his heritage. A redemptive element probably will be required, but it may need to be made manifest by others rather than himself. A new apotheosis perhaps.
He needs to become something new, not go back to who he was. There is an inherent similarity to the concept of Original Sin. Funny that!