How to remove imessage from ipod from computer [duplicate]

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• Steps after buying a used iPhone 2 answers

I sold my Ipod on Gumtree and the guy that wanted it gave it to his 9 year old Sister for Christmas.

On Christmas Eve it got a phonecall from him and he said that he is still receiving messages that i get sent - to the ipod aswell meaning he is receiving all my messages and personal info... Worrying.

My iphone i currently have its off as i lost my charger and so i need to solve this issue asap via my computer. How do i do it?

Any help appreciated. THanks