I understand you to mean that you want to move the x-axis over to the right. It can be done two ways. If you click in the graph you'll see the graph layer enclosed in a box with handles. Sretch the handle to the right to extend the axis, or set the Width field in dialog box Format:Layer:Size/Speed (tab).
This feature of adding an arrow at the end of the axis does not exist currently. Thanks for the suggestion and we will consider adding this in the future.
If you must add an arrow you can use the Line draw tool. This works well if you also hold down the shift key to force either a horizontal or vertical line. Otherwise in Labtalk use:
draw -l {x1,y1,x2,y2}; to draw a line from pt1 to pt2. Click on added line and select Properties from the Pull Down menu. This dialog box will let you add an arrow head to the line and alter params to suit your needs.