Cleaning a old copper boiler

[Finn peng]

Hello I have lately got out my old potstill, but my boiler was looking like it had seen better days,and its was covered in copper corrosion,what is the best way of cleaning up copper to make it safe to use again ,I tryed citric acid soak then scrubbef it with detergent and filled it with water and gave a good boil, is their any. Step I'm missing here looks usuable but still not perfect