Import and exporting the mapping file can be done from inside akeneo import and export jobs. Simple create a new Import/Export profile with the job called “Attribute values mapping import/export”

Here is an example of how a mapping file could look like.

attribute_code_akeneo attribute_code_gs1 select_option_akeneo select_option_gs1
ean_code 0_022
brand 3_003
colour 4_014 light_yellow YELLOW
colour 4_014 dark_brown BROWN


Beware all the akeneo attribute codes and GS1 attribute need to exist. Else the validator will provide you with validion feedback inside the step.