How should I cancel the vehicle registration?

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Last Friday, I received a letter from the local tag office asked for the tax payment for the trailer I previous owned. I guess that I didn't clarify this matter with the tag office previously, and I already gave away this trailer to my cousin. Now, I no longer own it. So, what should I do to avoid this tax payment? Should I need to go to the tag office, to file a cancellation on my registration at this matter? Or something else? Can anyone help?