This is likely misinterpreting the use case for left align. Depending on your flat file destination, it is not necessary or may be automatically performed by the destination application, such as Microsoft Excel file or CSV.

If you were to left-align your numerical values as if they were strings it would require casting them to strings and padding the strings on the left with spaces so all strings become the same length. This is computationally expensive, as you need to covert all rows in your dataset, and apply transformations to each individual record. Even worse, doing so will make the values unusable. Those strings will need to be converted back to numeric if you want to apply any computation to them, as strings cannot be used for calculations.

You'll be better off either ignoring the problem, or using your Excel file's built-in functionality to achieve this rather than writing bespoke code.