How to move a device from one site to another site?
You will need to configure the device to send logs to the new collector. For example if it is a linux host you would need to modify syslog to send the logs to the new collector hostname. For agentless windows you would just use the Manage Windows Service to add a new entry. It really depends on the kind of device you want to move, but either way the configuration needs to happen for that device.
Then you will have 2 versions of the device - the old entry for your previous collector and its new entry on the new collector. Historical data will be on the old collector.
You could export all of its data using lsdata and then re-inject it into the new collector if you like so all the data is in one place.