Download disk repair software like disk drills, photorec and Wondershare Recoverit. Not to overwrite, stop using the SD card. This can be discussed in the forum, where you can get ideas on what the best tool to use is and also get tips to increase the chances of recovering effectively depending on the type of camera or device you have.
For more help, You may also visit here -
https://forum.datarecovee.com/