Another easy way is to right click on the volume automation track header, then click select all. It should then select all volume automation points on that volume automation lane. In the top middle of the white rectangle that appears around the automation points, you should be able to grab the gray dot (scale vertically) in the top middle of the white rectangle and drag up or down. You have to be in the pointer tool and hover over the middle of the white rectangle to see the gray dot handle thingies.
You’ll notice this keeps an equal relative volume relationship in your automation data. That is, the dots get closer together vertically as your volume gets lower. This is actually usually desirable to keep relative volumes and to prevent really low levels from immediately bottoming out into silence.
These operations are so much easier than they used to be.