2010 Buick Lacrosse crank snsor where? Changing VVT snsors Help Locate all 4 ?

What is your question?

Car running rough.Code "VVT B1. Web. Suggest to locate and change all 4 VVT sensors crank sensor 6 iridium plugs 2010 Buick lacrosse 2,000,050 miles. I need help with location all 4 VVT also crank sensor.I see top and lower looks like two crank sensors and only found 1of4- VVT help easy best way to change these Please the web too general. Thankyou

What makes this problem better or worse?

Shortly After clearing codes vehicle runs rough codes return

How long has your 2010 Buick LaCrosse had this problem?

Few months.