AD sync not removing unwanted users and groups

I setup and Azure AD sync.

I made the mistake of following the wizard and syncing my whole AD. When I try to filter to sync only the OU I want in Azure, the erroneously synced groups and users don't go away in Azure when I try to apply a filter.

I found this locked thread https://social.technet.microsoft.com/Forums/en-US/e9cafccd-cea2-44af-b36c-13eaa0454c3c/dirsync-not-removing-nonsyncd-users?forum=windowsazureaditpro but it does not help me.

There are hundreds of unwanted users I don't want to remove them manually. someone help, or just tell me how to remove it all and start again.

CarolChi