1. Add a new series to your Bar/Line chart


2. Use the REPEAT() function to repeat the value you need
3. Use the COUNT() function wrapped around your Results Reference of the X-axis to count the number of points we need to repeat our value


4. Modify the Series' type into a "Line" via the Properties, and play around with the styling

**Another useful scenario would be to use the Average revenue or Average values of your main series, to calculate your Target value or Baseline value:


Useful Reference Links:
How to build a bar/line chart component
How to build a trendline in a bar/line chart