Excellent Fathi, having a better UI for axes will be very welcome.
Working with github (or any other git hosting such as gitlab) is a bit hard at first, but after a while it becomes very easy and practical. Tell us when you need help!
Regarding the fix, I think you can easily 1) go to https://github.com/FreeCAD/FreeCAD
2) Try to edit the file 3) github will propose you to fork FreeCAD and make the fix in your copy 4) After you do the fix, it will propose you to make a pull request. So I think it can be pretty easy.
I would encourage you to try that, so you'll already have all your github fork set up for you, but we can add your fix too if you prefer.