To force synchronization, log into your server that has the Directory Synchronization tool installed.
Open up Power Shell and navigate to C:\Program Files\Microsoft Online Directory Sync. as below
Start the Directory Sync Configuration Shell by typing .\DirSyncConfigShell.psc1
This will launch the Directory Synchronization Configuration Shell. Once this is open you can type the following command to force synchronization: Start-OnlineCoexistenceSync
Now to confirm that the Synchronization has run , you can check from the office 365 portal