If you'd like to adjust your labor costs for a specific project, you will first need to make sure this option is turned on in your company settings.
Go to Settings > Company > Labor Rates and you will see a section that says "Allow for Unique Labor Costs in Each Project". Select the checkbox in that section.
Now head back over to your project, and open the Project Details panel.
You will now see a Labor Costs column with editable fields. Just adjust the numbers as needed, and click "Save."
This will edit your labor costs for the current project only.
If you would like to edit your default labor rates (cost and/or prices) for the company, check out this article.
Hope that helps! Let us know if you have any questions.