There are a few things you can do.
Yes, you can lower the shooting sliders. This is the most direct and easiest thing to do. When you do that, look to see what type of shots are too successful. For example, if mid-range shots are about right but 3 pointers are way too successful lower the 3PT shooting slider but leave mid- range alone.
You can also raise Layup Defense Strength (Release) and Jump Shot Defense Strength (Release) for both the Human and CPU. Much like the shooting sliders, change the Layup slider for inside shots and the Jump Shot slider for mid-range and 3PT shots. Focus on the Release sliders and don't worry as much about the take off sliders to change shooting %. Be aware that it is somewhat counter-intuitive that changing the Human Defense slider affects the Human player while changing the CPU slider affects the CPU.
You can also adjust the Agility slider (higher value makes the players a little more responsive on defense), Offensive Awareness (lower values make the offense less disciplined), Defensive Awareness (lower values makes the defense less effective overall, has players make poorer decisions, leaves players open sometimes on switches and double teams, etc.), Offensive and Defensive Consistency (creating more or less consistent effective play and more runs).
If all you are trying to change is shooting % I would focus mostly on the Shooting sliders and the Defensive Release sliders because the other sliders have more gameplay implications than you may want to deal with.
When making adjustments, typically change only one or a few things at a time so you can see and understand the impact.
I hope this helps. Good luck.