User showing as "guest"

[nodle]

I have a user that shows as a "guest" he is not associated with any group. He was leftover from a import from IPB way back in the day. He later joined under a different name. All his post show but there is no account associated with him such as a user, banned, etc. He is just a "guest". Is there any way to associate this with an account so I can have control to say merge it with his other account etc.? Or has anyone else run into this problem and were able to resolve it? Thanks for the help.
User showing as "guest"

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