Post [Q] super su problem

I root my device (samsung galaxy s4), and install the super SU before, unfortunately my friend get my phone and made some changes, he UNINSTALL the SUPER SU improperly, and download/install it again, now I am opening my super SU and it says "THERE IS NO SU BINARY INSTALLED,AND SUPER SU CANNOT INSTALL IT. THIS IS A PROBLEM!", what should I do now?...please help.thank you.