Thanks for sharing your use case together with your query. That said, it is currently not possible to move an IoT Thing from one region to another. There would be a need to replicate these resources(Thing, certificate, policy) in the destination region as there is no option to transfer them to another region.
You can take a look at this AWS Solution for a guide in the replication flow. The use case is definitely different as this is for disaster recovery but you can check this out and see how the replication is achieved.
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