One option would be to use the "manage volume" feature. You'd request Cinder to "unmanage" it, manually move it and then request it to manage it back using the updated location.
You can ask Cinder to manage a volume by using the following (this is just a sample, replace those values accordingly):
cinder manage --id-type source-name hostName@backendName#optionalPoolName //share_host/share_name/file_name.vhdx
You can also get a list of volumes that can be imported by using "cinder manageable-list".
For what is worth, the Cinder volume migration feature doesn't work with the SMB driver since we're using vhd/x images while Cinder expects raw images or block devices. We did consider using qemu-nbd on Linux and allow migrating to/from most backend types but there were some security concerns from the Cinder community.
Regards,
Lucian Petrut