You can modify the position of trend lines by repositioning their start and end points, or by moving them to entirely new positions.
NOTE: To modify a trend line in the Chart window, you must display the Chart toolbar. To display the Chart toolbar, right-click the Chart window and select Show Toolbar from the Chart window pop-up menu. Click here for more information.
To modify a trend line, perform the following:
Perform the following to modify a trend line on the Chart window:
From the Chart
toolbar, click 
NOTE: If you do not see this button, you need to display
the Chart toolbar.
Perform one or more of the following:
To move the start
or end point of a trend line, hold the mouse over the start or end point
of the trend line until you see the Adjust
cursor
Hold down the mouse button and drag the point to
a new position and then release the mouse button.
To move a entire
trend line to a new position, hold the cursor over the trend line until
you the see Move
cursor. Click the mouse button and drag the trend line to
a new position, and then release the mouse button.