You can send polls to your residents at anytime, even after the virtual assembly has been concluded.
Click on the residential project that a virtual assembly has been hosted
Click on the virtual assembly icon
Click on an ended assembly
Click on the "polls" section in the header
Click on Launch poll in the top right corner of your polls
The poll will then be launched for everyone who has participated and residents will be able to access this section in their app. When you are satisfied with the results, simply click end poll.