I came across this video by Swapno.  In his video, he demonstrated how to shift focus while filming.  You can read from the description of the video how to do it.

I tried but I failed, for now.

I looked for a subject to try that.  However, I cannot seem to do it.  I found a subject, set up my camera and tried that.  I guess I have to look for more tutorial videos and try and try again until I can do what Swapno did.

Of note, I bookmarked his video.  When I opened the link, it shows his page but the his video is content is not his.  It was a video of something else I think by Xcorps.  Maybe it was just a glitch.

Here is the link to Swapno's video:  Shifting Focus