Since you’re already in Visual Studio, why not just simply write the code?
foreach (var f in new DirectoryInfo(@"...").GetFiles("*.cs", SearchOption.AllDirectories)) {
string s = File.ReadAllText(f.FullName);
File.WriteAllText (f.FullName, s, Encoding.UTF8);
}
Only three lines of code! I’m sure you can write this in less than a minute 🙂