Recommendation: Make sure to confirm the invitee's preference before voting for them.
To vote on a date/place for an event for an invitee:
Make sure the invitee is not invited to the event already. If so, just remove him/her: How to remove someone from a Vyte event?
On the top left corner of the event page, click on the "More" button
Click on "Share event"
Copy the link to the meeting (based on the goal of the event, if you want this event to be a group event or a 1-on-1 appointment)
Paste the link to a private or incognito browser window and make sure no one is logged on Vyte on this browser
Insert the info (name + email) of the invitee you want to vote for, and click on "Access this event"
You are now on the event page as your invitee. You can vote as that person by clicking on the date options.