Support for MPI parallelism in SpecTcl is an option selectable when SpecTcl is built and installed. You can see if MPI parallelism is enabled by looking at the VERSION file that is installed in the top level directory of the SpecTcl installtion (the INSTDIR directory in your tailored Makefile).
Below are the first two lines of this file for SpecTcl built with MPI support:
Example 1-1. VERSION file for SpecTcls with MPI support
Version: SpecTcl-7.0-000 build on RonDell Thu 06 Jun 2024 01:48:15 PM EDT by ron MPI Enabled
Compiled with /usr/opt/mpi/openmpi-4.0.1/bin/mpicxx and /usr/opt/mpi/openmpi-4.0.1/bin/mpicc
Towards the end of the first line you can see the text MPI Enabled. This indicates the installed SpecTcl was built with MPI support enabled. If MPI support was disabled, this will read MPI Disabled.
THe second line shows the compiler command used to build SpecTcl. Building software with MPI requires specific include directories and link libraries to be added to the compiler and linker flags. For convenience, MPI distributions such as OpenMPI and MPICH provide compiler drivers that define these flags for the user. Note that mpicxx is the MPI C++ compiler and mpicc the MPI C compiler. Mostly, take not of the path to the compiler. That will be needed both when you run SpecTcl in parallel mode and you may also need to define an environment variable to use SpecTcl in parallel mode.