So you need two ‘states’ for the menu which I assume you already have since you are obviously switching between them.
You just need to change the CSS for the ‘second/expanded state.
Looks like you are doing the expansion with JS/JQ…so it should be simple enough to toggle an additional class or adjust the CSS property from left to right.
Perhaps you could share that Jquery/CSS in a Codepen example…JSfiddle is little less…intuitive in that area.
Anyway, a JS issue…not a CSS one I think so I’ll push it over there for now.