I'm getting the error "This Steam account is already linked to another Plutonium account."

I linked my steam account to an old plutonium account, but I can no longer access that account and don't remember its login details.

I would like to recover the original account or find out whether the Steam link can be resolved so I can verify my games.

I can provide my Steam profile URL and other proof of ownership if needed.

Thank you for your help.