Hi Manivel Manickam,
Welcome to Microsoft Q&A forum.
As I understand, you want to restrict Azure Cosmos DB from public access.
Private Link allows users to access an Azure Cosmos DB account from within the virtual network or from any peered virtual network. Resources mapped to Private Link are also accessible on-premises over private peering through VPN or Azure ExpressRoute.
You can connect to an Azure Cosmos DB account configured with Private Link by using the automatic or manual approval method. To learn more, see the approval workflow section of the Private Link documentation.
This article describes how to set up private endpoints for Azure Cosmos DB transactional store. It assumes that you're using the automatic approval method. If you're using the analytical store, see Configure private endpoints for the analytical store.
Could you please provide more information on how you are trying to connect to the Azure Cosmos DB and also API, configuration, existing Network settings of your DB so that we can also check our end?
Thanks