To update the PLECS scope at a desired step response, you should set the "trigger channel", "sensitivity", "trigger level" and "trigger delay" parameters appropriately. To see a larger time span, increase the "number of samples" and/or "decimation" parameters. See the attached example.
This is explained in this video here -- https://youtu.be/zf6PtdZrc7w?t=246, at time stamp 4:06. Although this video is made for the TI C2000 target, the functionality is the same for the RT Box.
The scope results from real-time simulations can then be printed or exported from the File menu.