• Login into ESXi shell

• vmkfstools -i input output -d format -a adaptertype

eg:

vmkfstools -i “/vmfs/volumes/Datastore/examplevm/examplevm.vmdk” “/vmfs/volumes/Datastore2/newexamplevm/newexamplevm.vmdk” -d thin -a buslogic

Refer to

Cloning and converting virtual machine disks with vmkfstools (1028042)

Converting a virtual disk into a Raw Device Mapping (3443266)