How to get columns header of csv in custom import module

Hi I created custom module for import data by helping module ( https://github.com/Smile-SA/magento2-module-custom-entity-import-export)

In this case I need to get csv header names.
I tried several ways but it’s not working.

I tried getSource method but system gives source is not set .

If anyone know the answer please help me solve the issue

Thanks