Intel® oneAPI Math Kernel Library Developer Reference - Fortran
Normally, the only change needed to build your application with MPI FFTW wrappers replacing original FFTW3 library is to add Intel® oneAPI Math Kernel Library and the wrapper library at the link stage (see section "Linking Your Application with Intel® oneAPI Math Kernel Library" in the Intel® oneAPI Math Kernel Library Developer Guide).
When you are recompiling your application, add subdirectory include\fftw to the search path for header files to avoid FFTW3 version conflicts.