Look for modules that have been updated beyond the tagged versions used in SIMP 6.4.0-RC1
Verify all but most trivial of changes (e.g., documentation updates) are needed (ask in the Release Engineering chat room if you are not sure).
Verify the acceptance tests pass in GitLab and update the passed-pipeline URL on the SIMP 6.4.0 release confluence page (https://simp-project.atlassian.net/wiki/spaces/SD/pages/715784223/SIMP+6.4.0)
If they do not pass in GitLab, see if there is an existing bug ticket. It should already be noted in the SIMP 6.4.0 release confluence page
If you can't get them to pass in GitLab, but can get them to pass locally, enter a new bug report and enter that into the SIMP 6.4.0 release confluence page
Update the SIMP 6.4.0 confluence page with the desired tagged version and set 'GitHub Released' to no with a red cell fill