The coolant is not the issue. The issue is the problem that is causing what you call "overheating." At times, kids do not know what an overheat is. You also have not read the car manual. If you do not have one you can find one online for free. You could also ask at any auto parts store in the USA. But you must repair the "overheat" condition first. Allow a mechanic to do his professional best to find the problem. Once that is done, the coolant is added AND the motor oil must be changed.

Only use water, until you have figured out where the leak is, then replace all the coolant with the specified type. Adding coolant when you are not sure what is in it can cause a chemical reaction.

Your owners manual will specify a type of coolant.

A 50/50 mix boils at a lower temp than pure water if that tells you anything. Pure water is a booboo. Flush and refill so you know you are back to 50%.

No you can use any coolant .