This is the standard piece that explains how to use such a repair file safely. Steam Generic Repair Utility
Extract the contents of ft-fix-repair-steam-generic-rar to your desktop. Run the repair.exe or script file as an Administrator. Restart Steam once the process is complete. ft-fix-repair-steam-generic-rar
Because .rar files from unofficial sources can be risky, any "piece" written for this should include a security disclaimer: This is the standard piece that explains how