Update Building Plans in AutoCAD

I have construction drawings for my new house provided by the Architect in .dwg format.
We're making a change to the position of a soakaway. I have sketches provided by the builder showing the new location of the soakaway (see attachment). I need the .dwg files updated according to the sketch. When the .dwg file is updated, you'll need to generate a new .pdf to replace the existing drawing.
I've attached the original drawing (as .pdf) and the sketch showing the changes needed. The .dwg includes all the drawings of the house, not just this drainage plan.