You can use Data Migration Tool suggested on Automatic online backup and restore with Azure Cosmos DB article to do the same.
There is no way to take a backup and import to Azure CosmosDB.
The recommendation is to open a support ticket (e.g. via Azure Portal) or call Azure Support to streamline the backup/restore strategy and to request Azure to restore the latest backup in case of a disaster event. In addition, you can contact the Azure CosmosDB team by sending an email to AskCosmosDB@microsoft.com.
