Why are you even using a Replace? You should be getting the folder path from the user, making sure it exists or you create the path, then you append the filename to the path using Path.Combine().
string folderPath = Console.ReadLine();
if (!Directory.Exists(path)
{
try
{
....
}
catch (...)
{
}
}
folderPath = Path.Combine(folderPath, "export.txt");
...