To emphasize important data and create a narrative on a dashboard, a Platform Administrator should use a Text or Rich Text widget. This dashboard component allows for the addition of custom text, headings, and images directly onto the dashboard canvas. This functionality is specifically designed to provide context, explain the data presented in other components, and guide users' attention to key insights, thereby telling a more compelling data story as requested by the sales manager.

B. Assign a new Task to each rep: Assigning tasks is an activity management function used to track to-do items; it does not modify the visual presentation or narrative of a dashboard.

C. Use the Highlights Panel: The Highlights Panel is a component used on record pages (e.g., Account, Opportunity) to display key fields, not on a dashboard.

D. Send out a mass email: Sending an email is a communication method separate from the platform's reporting and dashboard features. It does not enhance the dashboard itself.

1. Salesforce Help Documentation, "Add Widgets to a Dashboard to Add Explanatory Text and Images": This document explicitly states, "Use a text or image widget to add context to your dashboard. For example, use a text widget to add a heading for a group of charts... Use another text widget to add a block of explanatory text that summarizes key takeaways." This directly supports using a text widget for storytelling.

2. Salesforce Help Documentation, "Lightning Experience Dashboard Components": This guide provides an overview of all available dashboard components. It lists "Text" as a widget type, describing its function as adding "rich text... to your dashboard," which is the mechanism for adding narrative.

3. Salesforce Help Documentation, "Customize Record Page Highlights": This source details the function and placement of the Highlights Panel, confirming it is a feature for record detail pages in the Lightning App Builder, not for dashboards. It states, "The highlights panel displays key fields for an object at the top of a record page."