Multithreading in geant4

hello everyone,
When I installed geant4 I used -DGEANT4_BUILD_MULTITHREADED=OFF, now when I run a program it takes much of time.
Can someone help me to set multithreading even if Geant4 is already installed with -DGEANT4_BUILD_MULTITHREADED=OFF.
thank you

If you used cmake interface, just reopen the build directory. the options that you defined at first will be appear automatically, Then you can just activate the Multithreaded option without changing the other options if you do not want to change, then reinstall the Geant4 again.


Thank you for your answer
How can reinstall it please