It would probably help if you told me how you tried to do it so I know whats wrong, but the way to do it, as I understand the method is click portal on the bar just below the banner up top, click on the dot next to the selection you want on the poll on the left hand side of the screen, and click vote. If thats what you're doing and it still isn't working, let me know, so I can try to figure out what's wrong.