In Excel Online, you can view charts that have trendlines or moving average lines, but you won’t be able to add or change them.
If you have the Excel desktop application, you can use the Open in Excel button to open your workbook to add or change trendlines and moving average lines there. Here’s how:
Click Open in Excel and add a trend or moving average line to a chart.
For news about the latest Excel Online updates, visit the Microsoft Excel blog.