This is a short one as it’s a PowerShell one-liner. But if it’s been a while since you’ve done this it may still be somewhat useful as the scheduled task used by DirSync in the old days is now gone.
Starting a manual Azure AD Connect can be done by connecting to the AAD Connect server and starting PowerShell.
To run a delta sync:
Start-ADSyncSyncCycle
To run a full sync:
Start-ADSyncSyncCycle -PolicyType Initial
After running one of the commands above you should see the synchronization steps being performed in “Synchronization Service” on the Azure AD Connect server.