Is it possible to add a microcopy into the Competencies section of performance evaluation?

Summary: Adding a text box to help the user adding a competency

Content (required): Our purpose is to add a textbox that appears whenever a user clicks on the Competency box (second picture), to help the user adding a competency (by creating a popup that says something like: "Type directly in the drop-down menu").

In the first picture there's an example of what we want for the Competency box.

How can we do this (if it's possible)?