How Do We Recreate Fat Files In Usb Pen Drive?

Recreate could mean a few things so I am going to work within the assumption that you have deleted or lost specific files from your drive that you wish to recover. There are two options to do this, but it depends on what created the data loss.

Option 1: If the files/entire drive was deleted or reformatted then it is a software based issue. In this case it is important to know that when files are "deleted" within computer systems they are only removed from the directory, and marked as writable. So if the data was not written over then it is salvageable, though if it has then it still may be partially. What you will need is a program like this (i think it's free but leave me a comment and i can find another if you want). Basically a program like this will recover data that has not been written over and will try to reconstruct the original file system on the drive

Option 2: If the entire drive has experienced an "environmental influence" (ie water or static electricity) then it is a hardware based issue. These issues usually present themselves after the unit is connected to the system and might be recognized when the system decribes the device as "unknown", "raw" with 0 bytes in size or "file system structure on the disk is corrupt and unusable". Data recovery for such drives usually requires unsoldering internal NAND chip(where the data is stored), cloning it using special flash reader device and using specialized software and algorithms to decipher image contents. This process takes a long time and requires a professional.