Use the undo tool 
from the Sketcher toolbox to undo your previous operation. For a diagram of the tools in the Sketcher toolbox, see “The Sketcher tools,” Section 19.4.1.
Depending on your previous action, clicking the undo tool can have the following effect:
Remove the object just created. Objects include sketch geometry (lines, arcs, circles, ellipses, fillets, splines, or points), construction geometry, or dimensions.
Restore the sketch to its state prior to the editing operation just performed. Editing operations include copying entities, deleting entities, moving vertices, trimming edges, extending edges, breaking edges, and changing dimensions.
Remove a retrieved stand-alone sketch, provided you have not positioned the sketch. Once you have positioned the retrieved sketch, clicking the undo tool moves the origin of the retrieved sketch back to the origin of the current sketch.
If you click the undo tool a second time, ABAQUS/CAE cancels the effect of the first undo operation. For example, if you sketch a line and click the undo tool, ABAQUS/CAE deletes the line. If you click the undo tool again, ABAQUS/CAE restores the line.
The undo tool does not undo view manipulation operations. For example, if you sketch a circle, magnify the view, and click the undo tool, ABAQUS/CAE deletes the circle (it does not resize the view).
