All citizens received an email with a notice to vote. If you did not get this email you should check your spam box or login to the RomanRepublic.org and check to see if the email you registered with the Roman Republic is correct here.
To vote in the Concilium Plebis read this.
To vote in the Comitia Centuriata read this.
All voting ends on June 18 at 2359 hrs (Rome time).