Ensure the bug was not already reported by searching on GitHub under Issues.
If you're unable to find an open issue addressing the problem, open a new one. Choose and follow the issue template to include as much relevant information as possible and or an executable test case demonstrating the expected behavior that is not occurring.
Open a new GitHub pull request with the patch.
Ensure the PR description clearly describes the problem and solution. Include the relevant issue number if applicable.
Suggest your change under GitHub Issues and start writing code. Send a PR when finished.
All information about building is here