Compilation file modification

Hi Minghao,
Thank you for publishing your own code. 

I don't fully understand the installation. In the guide you says "cd /opt/openfoam6/wmake/rules then open the file c and relpace the fifth line gcc with mpicc"

but I don't understand what is the c file in rules there are many other folders. Could you explain what file to modify to me?

Thank you!