You can use the following command to get and set the DFSR primary member.
Get which DFSR member is primary member
Dfsradmin Membership List /RGname:<replication group name> /attr:MemName,RFName,IsPrimary
Set the primary member for a replication group
dfsradmin Membership Set /RGName:<replication group name> /RFName:<replication folder name> /MemName:<primary member> /IsPrimary:True
Run "dfsrdiag pollad" to update Active Directory configuration.