What would you do if actual field installation does not conform to drawing?

Depends on who you are and what your position on this job is.

Why do you ask such a cryptic question?

A "design plan" is just that, a plan. Lines on a page can be drawn anywhere and look perfect. But when you get there, nothing works because, just for instance, no designer was told about the 40 ton safe and associated protective walling was in the way. Actually happened to me back in my puppy days.

You pick up this device called a telephone and call the responsible people before a tool ever leaves your bag. Get it right because if you don't, you get to re-do the work on your dime because, "you should have called".