The guides are easy: Please open at first an issue and where you will talk about the fix you want to do. The maintainers will periodically ask you how's the status of your contribution, to ensure features will come and to keep the repo clean.
After you are done, please do a pull request and the maintainers will take a look on it.
We don't guarantee that your contribution will take place into the stable release, that's what the maintainers have to consider.
If you have questions, before asking do take a look on the README which maybe solves your problem.