how can i select the correct file?

I am new to this field, so please explain to me how to select the correct file for download and remap/reflash ?

I don't know a whole lot about reflashing but what I do know is you are going to need to give more info.

If you wouldn't mind, please tell me this info:

What the year, make, and model of the vehicle is.

What map you need. If stock map: when you are reflashing, the stock map for your car will be on your car and you will be able to pull it off.