I ate hot/ warm oatmeal that had (cold) milk and butter with a PAREVE spoon by mistake. How can I make (Kashe) the spoon as PAREVE again? Can I place the spoon in boiling water using a pareve pot to KASHE it?
Yes you may use a pareve pot for this. Even if the spoon would need kashering, (which isn’t clear) it may be kashered in a pareve pot. The amount of absorbed taste that would come out of the spoon is minimal, therefore it will not cause the pareve pot to become milky.