Change the Tone Curve to allow it to behave as a draggable Point Curve
In Lightroom, you can make the Tone Curve behave as a Point Curve clicking the Click to edit the Point Curve indicator at the foot of the Tone Curve panel.
When a tone curve is set to be a point curve you can drag on any point on the curve to adjust the tones in the image at that correspond to that point on the curve.
With the point curve selected, click on the Targeted Adjustment Tool in the top of the Point Curve dialog and drag on the image to lighten or darken the image at that point. Drag upwards to lighten, down to darken.
To delete a point on the curve, hold your mouse over the point, right click (Command + Click on the Mac), and select Delete Control Point.