How to save a file that already exists?

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C#

I'm going to launch a code editor for people to create bots to disagree, it's almost all ready, but what I need help is when saving the file

What I have tried:

I created a function that saves but when the file already exists the person have to replace, then I created a String called currentFile that will store the path of the selected file, then how do I make it just replace the text inside the file without needing to replace the file or open the save menu?

String currentFile = "C:\\Program Files (x86)\\EXAMPLE\\FILE.js";
SaveFileDialog sfd = default(SaveFileDialog);
            if (fctb_code.Text.Length > 0)
            {
                sfd = new SaveFileDialog();

                sfd.ShowDialog();


                string location = currentFile;
                string sourcecode = fctb_code.Text;
                location = sfd.FileName;
                if (!object.ReferenceEquals(sfd.FileName, ""))
                {
                    using (System.IO.StreamWriter writer = new System.IO.StreamWriter(location, false))
                    {
                        writer.Write(sourcecode);
                        writer.Dispose();
                    }
                }