The reason I use this blog at times is to remember the issue I tend to for get and this s one of those commands
You can use the directory synchronization Windows PowerShell cmdlet to force synchronization. The cmdlet is installed when you install the Directory Synchronization tool.
On the computer that is running the Directory Synchronization tool, navigate to the directory synchronization installation folder. By default, it is located here: %programfiles%\Microsoft Online Directory Sync.
so just add the path to your environment variables and you can run DirSyncConfigShell.psc1 to open a Windows PowerShell window with the cmdlets loaded.
Then, type Start-OnlineCoexistenceSync, and then press ENTER.