snaphu is not an official part of SNAP, that’s why it is installed separately as a plugin. To use it for unwrapping via the command line you have to add the snaphu\bin folder to your system’s PATH, then you can simply execute the command inside the snaphu.conf file in the folder where you exported the data.
an example is given here: https://www.youtube.com/watch?v=w6ilV74r2RQ (starting at around 43 minutes)