Hello!
I have checked your link, and it gives me the WordPress installation page.
Here are tips when you are editing any WordPress core files (or plugins’ or themes’ files):
Whenever you want to make any changes, make sure that you have a copy of — the original file, in case of anything goes wrong, you have a backup so you can quickly put it back, so you have time to find the error, ad in the meaintime, your site works well.
– I dont recommend using the built-in WordPress code editor for php files, mainly because if you have a syntax error in your code, it could break the site so badly that you could not use the editor again to change it back
– the WordPress editor does not have code highlighting and it’s missing an undo button
So my recommendation is: use some code editor on your computer, download the file what you want to edit, make a copy of the original one, and when you are finished with editing, just upload the file back to the server with ftp.
If you have any additional questions, just post them here.
Have a nice day!
Greetings,
Balint