For now, migration from panel is not possible.
You can create a new vps on Virtualizor panel and then stop it and manually move old vps disk to Virtualizor server from Proxmox server.
You will need to replace the new vps disk with the old one keeping the same naming as per the old disk.
Note : Virtualizor may fail to perform operations on such vm since old disk is not created using our OS template.