When ever you need to migrate to from one vCenter instance to another there are lots of things you need to migrate.
This PowerCLI script will help you migrate members from one DRS VM group to another. It can easily be modified to be part of a bigger context, or migrate all groups available.
The prerequisites are that you have both the new and the old vCenter running, and that you have disconnected you hosts in the old vCenter and connected them to the new one. Do NOT remove them from you old vCenter. Leave them disconnected.
The purpose of this script is to migrate from one vCenter to another when using dvSwitches. The dvSwitch is bound to vCenter, so in order to migrate hosts from one vCenter to another you can map the networks using this script. All you need to do is disconnect the host from the original vCenter with the VMs still running, but not remove it. Then you connect it to the new vCenter.
When upgrading to vSphere 7 or any other version, you might choose to create a brand new vCenter instead of migrating the old one. But what about folder structure, tags, distributed switches and so on.
Here I will demonstrate how you can easily migrate your tags from one vCenter to another using VMware PowerCLI.