Hello and welcome to Just Answer, my name is Matt.
Sorry to hear about your problem...this is unfortunate.
Years ago, when engines were made of cast-iron, you could overheat them pretty good, then repair the coolant leak, and get back on the road.
Modern engines are usually aluminum, which is more easily damaged by overheating. Aluminum expands more when overheated.
The excessive expansion can warp the cylinder head an cause head gasket failure.
And usually head gasket failure leads to more severe overheating.
Here's what the dealer technician should do......
Remove the cylinder head. Then they will use a precision straight-edge tool and feeler gauges to measure the warpage of the cylinder head sealing surface. If it is warped beyond specs, then the cylinder head must be replaced.
They will also use the same method to check the block (where the cylinder head mates to the block). If it is warped beyond specs, then the engine must be replaced.
If you are lucky, only a new head gasket will be required.
But most likely, it will need a new cylinder head as well.
It is possible thatt he car has this problem when you bought it. Many times, cars are traded in when they have an expensive problem, or a problem that is difficult to solve.