-Pick your surface in the drawing and right click and select Surface Properties.

-Select the Analysis Tab first, then go to the Analysis type and select from the list User Defined Contours.

-Go down to where it says Ranges and put 1 in there and then on the right hit the run analysis arrow and at the bottom you will see a level range come up. Go to the elevation and pick in there and set it to the elevation that you require and then click on OK to apply it.

-pick the surface on the screen again, right click and this time go Edit Surface Style and go to the Display Tab, make sure that your User Defined Contour has the light bulb turned on.

Make sure you Thaw or turn on all layers especially if the user defined contour is on a layer that is either frozen or turned off.

Your user defined contour should now being showing on the screen. Change the color of that contour in Edit Surface Style.