If you are not registered to vote, the deadlines to register are July 8 for the Aug. 4 primary and Oct. 7 for the Nov. 3 general election.
On the Missouri Secretary of State website, the Voter Lookup uses the exact data you provided when you registered to vote. It is a bit tricky. But you can try many times to find yourself on the voter rolls. If you are still unsuccessful but believe that you are registered to vote, contact your local election authority.