Unless you have a Time Machine backup of that overwritten original file, or have it on another storage medium, then it is gone with no recovery possible. The Finder would have warned you about the overwrite condition and offered to keep both before you ignored it and doomed that original file.
Make a copy of or rename the now overwritten file so that Time Machine will not overwrite it with the original restored copy.
If you do have a Time Machine backup prior to the original file overwrite, visit the Time Machine icon in your menu bar and select Browse Time Machine Backups. Go back to a time prior to the overwrite event in the same location in the Time Machine interface, locate the original file (it will respond to a Quick Look to confirm its originality), select the file and click restore.