Is it possible to change a CSS pseudo element in JS?

This is my CSS code

.lang-menu .selected-lang:before {
    content: "";
    display: inline-block;
    width: 24px;
    height: 24px;
    background-image: url(../img/icons/armenia-flag-round-icon-32.png);
    background-size: contain;
    background-repeat: no-repeat;
}

Here is my JS code

function changeCss() {
let elem = window.getComputedStyle(selLang, ':before');
elem.backgroundImage = "url(../img/icons/united-states-of-america-flag-round-icon-32.png'))"
}
changeCss()