You don't need to define IFPP and MYTASK in your user subroutines. They are defined when Autodyn starts to solve and are then passed to MDPP. See attached pictures below.
When the box "Activate Parallel Processing" is checked, IFPP = 1. Otherwise IFPP = 0. "MYTASK" is the task number. It is assigned by Autodyn automatically during runtime.
Once an Autodyn user subroutine is integrated into Autodyn user executable, Autodyn will automatically incorporate it into parallel processing scheme. User don't need to do anything while writing the user subroutines.
Furthmore, to start Autodyn with parallel processing, a command of AutodynWrapper.exe or a user-defined configuration file "applfile" is needed. The total number of workers is defined in the command or applfile and is then passed to the module MDPP.
More information about how to use AutodynWrapper.exe can be found from ANSYS HELP in the Section 22.1 Running Autodyn on Windows Platforms under Autodyn User's Manual.
More information about how to use applfile can be found from ANSYS HELP in the Section 3.1.1 Running Autodyn with Intel MPI under Autodyn Parallel Processing Guide.