DOE can be used to implement Response surface methodology to create emperical mathematical model for response in terms of design variable. This model can be optimized to get extereme response by any unconstrained optimization algorithm.
Try practising using design expert trial version. First look out for YouTube tutorial videos. ensure you follow each and every step as mentioned in video. Since its new to you try practising with data that are already available in previous research articles. Practice with those data nd verify your result with one in those articles. I guess this should help you