This is not a question of code. Sliders are "targets", ie graphical objects made using the MakeTarget tool. No knowledge of programming is required. See
https://www.youtube.com/watch?v=3tqSdHitr9c for an explanation of the concepts and
https://www.youtube.com/watch?v=xATm4zRloPQ for more practical instructions.
The targets bundled with MakeHuman is only a base set. If your needs cannot be solved with these, your options are to either download a third part target from the asset repos or to model a new target of your own.