This answer applies to Trade Interceptor for iPhone, iPad, Android Tablets, Android Phones, Kindle Fire and BlackBerry Playbook.
Select the icon "Tools list" from the bottom menu bar on the tablet. On phones, first switch to the tools bar by tapping on the first icon on the left then select "Tools list".
Select the trend line.
Touch the chart and draw it on the screen.
When you are finished,the line will still be active so you can adjust its ends or displace it laterally by dragging the body of the line.To exit the drawing mode switch back to the charting bar using the icon on the left.