What action should be performed to add new field values from a loop in Salesforce?

To add new field values from a loop in Salesforce, utilizing the Assignment element during the iteration is the most effective approach. The Assignment element allows you to modify variables and can be used to update field values for records within each iteration of the loop. By incorporating the Assignment element, you can assign new values to your variables or create new records as the loop processes each item, ensuring that the necessary values are captured dynamically at each step of the loop.

In contrast, while a Record variable is useful for storing data related to a single record, it does not independently facilitate the addition of field values during the loop. The Loop element itself is essential for iterating through a collection but does not provide a mechanism to change values. Lastly, adding a separate input field is not relevant in the context of processing collections within a loop, as this option does not align with the inherent functions of loop iteration in Salesforce automation processes. Therefore, utilizing the Assignment element during the iteration is the best choice for effectively managing and updating field values.