If your really having trouble thinking of things to say or commentating in general then jot down some topics on a sticky note to talk about throughout the video. Plan your video ahead of time, have a general idea of where your character is going or what your going to be doing during that gameplay. This will make it easier to multi task your gameplay as well as speaking. Some people are talkative naturally but generally though the more you commentate it will start to come naturally and you won't be needing any help at all in no time. I'm calm by nature and have been the type of person to never really speak back so when I started commentating I was struggling to commentate for 2 minutes without being speechless as to what I should say next, now I can sit there and speak for 20 minutes about my bloody socks. Don't try to impersonate someone else, you can try acting a persona (obviously being intentional for entertainment not imitating someone) or just talk the way you normally would if you imagine you were sitting in an environment your most comfortable with to get rid of any stage fright you may have. Try to commentate as much as you can, obviously if you want the viewer to watch a cutscene instead of commentating then by all means do that but don't leave out pauses that will seem out of sync and unnatural during the video. Also speak about things that you have the most knowledge in, things your passionate about through the video. You will find that speaking about things you most enjoy will make for easy commentary.
P.S fix that channel link of yours brah