Select the chart
Click the data series you want to analyze
Right-click the selected series
Click Add Trendline
Choose the trendline type you want
Format the trendline if needed
Close the formatting pane when finished
Select the chart
Click the data series you want to analyze
Right-click the selected series
Click Add Trendline
Choose the trendline type you want
Format the trendline if needed
Close the formatting pane when finished