Bialyhoo22 described the voting process for the original production (which I saw twice).
Members of the cast, with the exception of everyone who is a suspect (since they remain onstage and hold up numbered cards) go out into the audience. Each remaining cast member is assigned a section in the house of roughly 50-100 people. They interact with the audience and count the votes for that section, then return to the stage. The votes for each section are tallied backstage and then they resume the play. As the plot continues to unfold, the audience's choice for the murderer and the "mystery detective" are both revealed within the action.
Not saying that's exactly how it will be done in the revival, but it's how they did it in the original.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22