This is a variation on a question we are often asked.
Short answer: The Steinberger material model does not include a parameterisation of melt transport. Implementation would require a significant change to the code, not just the prm file. Any implementation would need to carefully consider the chemistry and physics of interest.
Longer answer: See previous posts on this topic, including the three links below (which you can find by typing “melt” into the search button in the top right of the forum page). The first post from Juliane is particularly relevant. I think her question is also useful here:
What is the purpose of your model, and what specific components/physical processes do you need for that? For example, is it important to see where the melt migrates to, or only where it is being generated?"
If we have more details on exactly what you want to do, we can suggest (a) existing material models, or (b) the easiest way to implement what you want.