Use Initial Stitch edit box to select stitches within an Object. Initial Stitch is first stitch of selection. Last stitch is given by Ending Stitch. Selection is drawn in red color. It may be cut out by Split command, and then manipulated as independent Object. This edit box is enabled in Select Mode only, in case that there is just one Object selected.
Another way of stitches selection is to use Freehand Select Mode.