You cannot change column names because it is important that the columns be easily tracible to the fields in the API documentation provided by each data source.
We want to avoid a situation in which there is confusion about which field has which values, and make it clear that Flatly preserves the data from its true, original structure from the data source API.
Workaround: However, you can use downstream tools to customize column names, like Tableau, Looker Studio or Power BI.