Thank you in advance for contributing to DeepVariant-on-Spark!
You can just let your code do the talking for you if you like.
Before you write too much code, check the open issues in the DeepVariant-on-Spark issue tracker and DeepVariant-on-Spark open pull requests to see if someone else is already working on it. If the issue is a new one, and you have already written the code to address the issue, simply submit a pull request. If you haven't written any code but plan to, go ahead and open a new issue and assign it to yourself to socialize your work. When you submit your PR, please reference this pull request so that it will be automatically closed when the PR is merged.
The issue tracker has a list of "pick me up!" issues that are good tasks to help you get familiar with DeepVariant-on-Spark; they don't require an understanding of genomics and are fairly limited in scope.
Github provides a nice overview on how to create a pull request.