The OpenVPMS source is hosted at bitbucket.org, at https://bitbucket.org/OpenVPMS/openvpms
To contribute a change to OpenVPMS:
For a tutorial on the Bitbucket workflow, see https://www.atlassian.com/git/tutorials/learn-about-code-review-in-bitbu...
For a general tutorial on Git, see https://www.atlassian.com/git/tutorials/learn-git-with-bitbucket-cloud