If you are opening the pop up window using window.open, then you can clsoe it as well using the following :

https://developer.mozilla.org/en-US/docs/Web/API/Window/close

//Global var to store a reference to the opened window
var openedWindow;

function openWindow() {
  openedWindow = window.open('moreinfo.htm');
}

function closeOpenedWindow() {
  openedWindow.close();
}