Lower Autoplay Video Volume

I am embedding a video on my page and using autoplay feature, however, I want to be sure the volume is automatically lowered. I know there is probable a CSS code that does this. I found the following code but I need to use my block ID and can't figure out how.

#block-yui_3_17_2_1_1590117024504_74511

/* video volume on auto */
{var video=document.getElementById(#block-yui_3_17_2_1_1590117024504_74511);
  video.volume=0.1;}

Can you share link to page where you use video?

or use this tool to find block id. https://chrome.google.com/webstore/detail/squarespace-collectionblo/bggpdfnccodbnmcndckmeehdjkjojkde

The block ID is: #block-yui_3_17_2_1_1590117024504_74511

I inserted it in the snippet of code I pasted but it looks like it's searching for an element ID.