The scroll X is the element that enables you to scroll on a page from left to right, that is, horizontally. You can see it when there is a horizontal scrolling bar on the browser. It happens when the content doesn’t adapt to the size of the screen meaning that the site is bigger than the screen window and it indicates that the website is not responsive enough.
The presence of a scroll X has a bad influence on users' experience: horizontal scrolling is not genuine for users, they don’t have the reflex to scroll pages from left to right. If users have a bad experience on your site, they are probably going to return to SERP to choose a more adapted website increasing your bounce rate, and this will influence directly your ranking emplacement.
You need to work on the CSS style/ template of your page.