Add your name to the list on this wiki page (with any comments about your availability). If you want to join after the sprint has started just join the IRC channel: #openmrs , and say hello.
The general process:
New to OpenMRS sprints? Want help getting started? Join IRC on the #openmrs channel, and say "???": I'd like to participate in Cohort Builder sprint 16!”. If you get no response, just ping any of the above sprint participants as per the IRC tips at https://booki.flossmanuals.net/openmrs-developers-guide/support
Set Up. See our HOWTO for how to set up on git, how to make a PR, and a few other cool tips to get you all set and ready to start participating in the sprint. Feel free to reach out to any of the participants listed above, for help on setting up where unclear(We are happy to help!).