The first step is to find your save data folder:
* Open the world selection menu, select "manage world" of your corrupted world (the wrench button), select "Open world folder".

The second step is to locate the files to repair:
* Open master/save/session, then open the last folder with random name. The files are the one starting with 00000, and without the .meta extension.
* Alternatively, you can use the Windows search bar with 00000.

The final step is to repair the files:
* Open each file in any text editor, Notepad for example, search all instances of the word "loadstring" and replace them with nothing. (Ctrl + H in Notepad). Save and close the file.
Generally, only the file with the highest number contains loadstring.