"Let's assume you have a VM called examplevm that you want to
reuse on this host. On the old host, you should have a directory
Machines/examplevm in the VirtualBox directory; Machines/examplevm
should contain the examplevm.xml file. Copy the examplevm directory
(including the examplevm.xml file) to your new Machines directory
(if your user name is admin, this is
/home/admin/.VirtualBox/Machines - the result should be
/home/admin/.VirtualBox/Machines/examplevm/examplevm.xml).
"In addition to that copy the examplevm.vdi file from the old
VDI directory to the new one (e.g.
/home/admin/.VirtualBox/VDI/examplevm.vdi). Afterwards, you must
register the imported VM: