An update transformation allows us to do a quick VLOOKUP between two datasets and replace the existing column. Let's say that you extracted accounts from Salesforce and now the account names have changed, and you want to quickly change the names in the existing dataset. You can do this via the update transformation. The working example for this section is shown in the official documents (https://help.salesforce.com/articleView?id=bi_integrate_update_transformation.htm&type=0&language=en_US&release=206.19).
You can use a combination of these operations in the dataflow.json file to transform your dataset.