You mean like this? https://forum.mendix.com/questions/9019/Glyphicon-right-on-button-instead-of-left

The mentioned solution will apply to all your buttons, but if you add your own class to the specific button you want to target, it should turn out the way you want.

So something like

.btnRight > img, .btnRight > .glyphicon {
    float: right;
}