If you need to clear the current selection of triangles on a mesh or points on a point cloud, go to the Select tab and click Clear Selections.
For example, in the screenshot below the Select Primitives workflow is active, and a group of mesh triangles has already been selected with the Lasso mode. If this selection is no longer needed, click Clear Selections or press Command + X (Ctrl + X on Windows) to remove the current selection and return the mesh to its unselected state.
After you click Clear Selections, the current primitive selection is removed, but the Select Primitives workflow remains active. You can then begin selecting new triangles or points right away.
How to Use the Clear Selections Tool