First, the data is still where it was before the formatting.
If the files are unique and non replaceable, I would suggest to clone the drive and work on that image to be safe if you make a mistake.
The SD card most likely has a FAT format. That means it could be very simple to restore the partition and its directory with only the very last file operation to mess up the file directory.
Or in worst case it could be a tedious task to match together sectors of the file. A good start would be to know the file size and the file format,
Plain text files is usually the easiest to find and restore.
So what tool do you know best. Are you familiar with the Command Line interface or would you prefer a graphical interface?
What OS do you have?