If you have customized the Slope Limits with the Define Limits or Move Limits options, you can use the Reset to Default option in the Slope Limits sub-menu of the Surfaces menu, to reset the Slope Limits to the default limits which are calculated by Slide2. The default limits are based on the geometry of the External Boundary, and will generally be at the upper left and right corners of the External Boundary.

The Reset button in the Define Slope Limits dialog can also be used to reset the Slope Limits.
The Reset option is also available if you right-click on a Slope Limit marker.
The slope limits will automatically be reset if any editing is performed on the External Boundary (e.g. adding, deleting or moving vertices).