How can the distributed firewall rules of NSX-V（6.3.7） be converted into NSX-T（3.0.X） format quickly and in batches?
A little birdy told me that this is something that the migration coordinator should be able to do. Whether it's "quick" or "in batches" I'm not sure. YMMV.
As Daph said, the coordinator does that.
Check this video it shows the entire process:
Demo of VMware NSX-T Migration Coordinator - YouTube