Indeed, this is only to tune existing positions.
Start by adding your various grids with the panel iEEG, in the MRI viewer, as illustrated in the tutorial.
Then use this 3D view to modify the positions.
Note that I’ve been fixing many bugs related with ECOG in the past few days, and I will do a few more edits today. Start by updating Brainstorm, and keep an eye on the updates log: http://neuroimage.usc.edu/brainstorm/Updates