I don't have one so I am not sure how detailed the process is to strip it down. Based on what I have seen the grips are removable, so I would take them off, lock the slide back, brush away any fouling/grime/residue you can, then use a cleaning spray to break up and blow out anything that remains, if it is really bad, try soaking it for a while then use a nylon brush to clean away anything that has been broken loose.
Once it has been cleaned, you should be able to apply oil/grease and then cycle the slide back and forth to try and spread it.