Can one please let me know on How to disable the publicNetworkAccess for the existing cosmos database.
This is to make sure that the cosmos database is not exposed on the public network and will be configuring a private endpoint to restrict the access of the resource.
You could use the az cli command: az cosmosdb update to disable the publicNetworkAccess for the existing cosmos database.
az cosmosdb update --name MyCosmosDBDatabaseAccount --resource-group MyResourceGroup --enable-public-network false
According to Docs,
To make sure that public network access is disabled even before the creation of private endpoints, you can set the publicNetworkAccess flag to Disabled during account creation
Here is an example
Also note
Note that this flag takes precedence over any IP or virtual network rule; all public and virtual network traffic is blocked when the flag is set to Disabled, even if the source IP or virtual network is allowed in the firewall configuration.
You should be able to update this setting on the portal. Please see the screenshot below.
