Trimming videos using Apple’s photo app

According to Apple’s help documents I should be able to trim my videos straight away in the photos app. According to the help doc This is done by pressing Edit and dragging the left and/or right ends of the video clip inward.

This works fine for trimming the right side (tail end of video clip). However, I am unable to drag the left side so as to trim off some portion of the beginning of the video clip.

I have an iPhoneXS and all my apps OS is up to date.