The first treatment is a job you need to do, in changing your lifestyle. Such things as stop smoking (if you smoke), eat healthy foods, lower your saturated fat intake, exercise regular, ensure your blood pressure/cholesterol levels are under control.
We could sit here and give opinions on what should be done to your vessels, but we have nothing to go on. For example, do you have any symptoms? How do you feel if you exercise? what medication do you currently take?
IF you have shortness of breath/chest pains with exertion, and this is with the use of medication, then I would be interested to know what your Cardiologist suggests. There are only 2 options left, bypass or angioplasty (stenting). I can't see a bypass of the 80% blockage lasting very long because the area further down where the graft needs to be made is diseased.
What they should have done is used an FFR catheter to establish which blockages are causing the most resistance. It could be the 30% or the 80% or both. The left stem is important because it obviously gives the supply to the LAD and the LCX arteries. Any restriction here will affect those two very important vessels which feed your left ventricle.