YOU CAN NOT EDIT OR PLACE BLOCKS IN DEBUG MODE
okay a quick summary of debug mode is a world with nothing in it except every block there is on miencraft okay so all you have to do is head over onto single player click on more world options shit and click on world type untill it comes up with World Type: Debug Mode thats it guys
if you found this tutorial helpfull be sure to leave a diamond and post in the comments section delow what you want next thanks.