You can check here to see if you are registered. Also has a link for the application to mail in. https://www.sos.mo.gov/elections/VoterLookup/default.aspx
Missouri was a primary state, but the GOP here elected to go to a caucus. Because the rules had to be sorted out we got the caucus, but the primary had already been scheduled. Missouri will still have the primary for show, but the caucus will count for delegates.
In MO too but not too sure I understand what the difference between the primary and the caucus is either. Can we participate in both? Wierd this year.