[checks latest VMworld Updates...]
It's called the vCenter Server Converge Tool
https://blogs.vmware.com/vsphere/2018/08/under-the-hood-vsphere-6-7-update-1.html
Essentially, you have to go with the in-place upgrade to 6.7 U1, then run the vCenter Server Converge Tool to move your external PSC data to the embedded PSC, lastly decommissioning your external PSC.
