Found old water pipes while tearing down walls in an old house renovation today. How do I handle the change order process steadily?

Today, after opening up a wall during a kitchen renovation, we discovered old galvanized pipes that weren't in the original scope. The homeowner was immediately worried about the budget spiraling out of control, and the workers wanted to keep tearing things down. I first had the site secured, took clear photos of the pipe locations and the extent of the corrosion, and then contacted a plumber to…