The documentation in BAW 20.0.0.1 has improved the section on synchronization of users and groups -- with a few updates to command-line commands in this later release, but I think this is the best reference for you.
Synchronizing users and groups
https://www.ibm.com/support/knowledgecenter/SS8JB4_20.x/com.ibm.wbpm.admin.doc/topics/sync_users_and_groups.html
Upon re-reading your question, however, I see this is not what you are asking about. Here is answer to your question:
There is no specific feature to synchronize BPM groups created in your Process Center to your Process Servers. This synchronization will happen automagically if you have a BPM group as a "Standard Member" of a Team definition -- and then deploy a snapshot of a Process App containing that Team to a Process Server.
During the deployment (import) of the Process App to the Process Server - BPM will create the necessary objects (including BPM groups) to satisfy Team definition references. In fact, if you have a Team defined on your Process Center that uses an LDAP group -- and that LDAP group is not available on your Process Server, the deploy (import) process will create a BPM group with the same name as the missing LDAP group to satisfy that Team reference.
In both cases, if you examine the group using the "Group Details" of the BPM REST API Tester (URL: /bpmrest-ui ) you would see a description of:
'Auto generated during snapshot installment'
#BusinessProcessManager(BPM)#Support#SupportMigration