To expand on my answer in the comments.
“DEFINES” are constants that can only be defined once. If you could change the value of a constant, then it wouldn’t be a ‘constant’.
So, the issue is that once defined, the constants that you added cannot be redefined to other values.
It is not clear from your question where you are adding those lines, but they are probably somewhere after the constants were previously defined. If you need to change their values, then look for their original location (the place where they were initially defined). If needed, take a look at an unmodified wp-config.php file (from a fresh installation) and see where those were defined.
I’m not a big fan of changing things in the wp-config.php file from their original values. There has to be a really good reason to change things in there.
(Many times you will see advice to change the URL in the wp-config.php file, rather than changing it in the wp-options table where it supposed to be changed. I never see a good reason to change the URL in the wp-config.php file if it is properly specified in the wp-options table. But, I digress.)