Before & After Slider - But not 50/50

Hey Forum, 

So I have this awesome before & after slider (https://www.will-myers.com/products/p/before-/-after-image-slider) from Will Myers, and while I thought it had the function to choose where the line that dividends the two images started, it, unfortunately, doesn't and the team wasn't able to help with this. 

So I was wondering if anyone had input to help me so the slider could start more to the left, so it reveals more the after. 

Many thanks for anyone taking the time to read, and/or help.