2) dev blog from Theo who is Program Manager, Azure Cosmos DB =>https://devblogs.microsoft.com/cosmosdb/how-to-change-your-partition-key/
The good news is that there are two features, the Change Feed Processor and Bulk Executor Library, in Azure Cosmos DB that can be leveraged to achieve a live migration of your data from one container to another. This allows you to re-distribute your data to match the desired new partition key scheme, and make the relevant application changes afterwards, thus achieving the effect of “updating your partition key”.
You will need to have access to an Azure subscription, and an Azure Cosmos DB SQL API account that will be used for the migration metadata (this can be the same as the collection where you wish to change partition key scheme, if you wish).
The deployment uses Azure Resource Manager (ARM) to deploy two app service plans. One is for a client node.js application, and the other is to handle the migration workload and Change Feed processing.