Note: any reference to pipelines is meant for users that are developers. If you are not a developer, just skip over that word. 🙂
Data Helpers are used to modify data from the way it is in the source document when data is exported. For example, you may want to converts all times to UTC time so they are harmonized (e.g. 12/15/2022 become 2022-12-15T00:00:00.00000. Or some countries use a comma for the decimal indicator. You may wish to replace the comma with a decimal and get rid of any thousands indicators (e.g. 12,456.20 becomes 12456.20)
You can get to a Data Helper by ensuring that your project either has the PDF Assistant or has a pipeline containing Data Helpers. The option to add a helper will then be available under properties on a label you are applying in training.