After you open the charm window, move it so it is not in front of the inventory window (you can move the inventory window partly off screen if required). When you click on a charm to drag and drop it, that brings the inventory window to the front, which can cover the charm window you need access to.

charm effects


BTW, the BD forums are above the DD forums, and below the D2:ED forums in the main index list. If you are signed in there are + or - buttons at the right of each main forum group; click the - button for a group you don't have the inclination or language skills to follow, and it will collapse to a single line, making it easier to see the groups you do wish to follow.