Open WinRAR application
1. Click on file, and then select open
2. A find archive window will be opened, select corrupt rar file from your system
3. Click on open button
4. Press Alt+R
5. Repairing File Name.rar will be opened
6. Click on "browse" to save repaired file at desired location
7. Check Treat the corrupt archive as RAR box, and then click OK
8. After corrupt RAR archive is repaired, click on close.
Or, you can also use third-party tools like RAR Fix Toolbox or recovery toolbox for RAR. They usually can repair highly corrupted files.