On the Engaging Networks Mapping interface there is an filter to handle 'Decode values'.
This is effectively a 'value' replacement tool. On processing of the mapping - the respective Engaging Networks Import Record field, set as the Decode Value, would have it's value replaced if it matches the specified criteria.
Note: this does not replace the value on the Engaging Networks Import Record itself. It only replaces the value on processing.
In the examples above, the following fields are listed.
The reason this format is required is because it is matching the field name under the Components Mapping. You will note that two fields have the namspace but work_phone does not. This is because 'work_phone__c' is a custom field, added to the Engaging Networks Import Record. For fields included in the package installation, use the full API name.
You can find the relevant Component Mapping by heading to Mapping Templates > 'Respective mapping' and then isolating the field for the component. There you shall see the 'EN Field To Import' option.