first, your qualified tradesman has made a major, dangerous f**kup. You should call them and abuse them tomorrow.
It is easy enough to bolt the calipers back up properly, you just need the right size spanner or socket (preferably on a 1/2" drive).
Don't drive the car until it is fixed, you are likely to lose your brakes entirely.
On second reading, I am not sure you mean the caliper mounting bolt - can you post a pic?