Insider TA allows you to insert up to three trend markers for each stock view, using the cluster of 3 buttons labeled "Trend Lines". After clicking one of these buttons, you will be prompted to click and drag a line in the box chart. Actually, two trend lines will be drawn, but the 2nd trend line is directly on top of the first. You will also observe three tiny yellow handles: A square, diamond, and circle (initially, the diamond will appear on top of the square). Each of these handles can be grabbed and dragged with the mouse:
Using these handles, you can manipulate the trend line to any desired position, as illustrated here.