In the thumbnail view of your zeeting, you'll unsurprisingly see a thumbnail of each poll in that zeeting. Look closer and you'll notice that in the top right-hand corner of each thumbnail there is a grey checkbox.
1) Select the checkbox of the poll you want to copy and a "Copy" button will appear at the top of the screen.
2) Select the copy button.
A duplicate of the poll will be added to the end of your zeeting.