This are not two new files. This two files are in the folder
admin/credits
Download the two files and make a copy of the files.
After this you can insert the updated code in your own
files. After the changes you must upload the modified
files in the folder back.
Then you can make a test.
Submit with empty user fields = error message
Submit with both filled out user fields = error message.
Then you can give a demo user credits to see if it work.
If you have this done, we must insert the language file
and adjust the mysql query.
Greetings
Alfred