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There is a AD connect tool that is used to sync object's from on-premise to Azure AD.
However, Azure AD connect doesn't sync from azure AD to on prem, normally Azure AD connect is used to synchronize an on-premises environment to the cloud.
The only option is to export users from Azure AD, and then do a bulk import into Active Directory, but you will need to reset the passwords.
Apart from this you could also create new users in On-premise AD.
And also you cannot manage users in Azure AD and because as mentioned because there is no tool that can sync from Azure AD to on-premise AD.
Let me know if you have any questions.
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