Exchange 2013 search fails

Hi experts,

So I often get users asking about their emails they can't find and I know that the index has failed yet again.

I found this article that seems to be explaining the issue and resolution but I'm having troubles executing it

http://support.microsoft.com/kb/2807668/en-US

I don't understand this point
Create a new Active Directory group that is named "ContentSubmitters" and then grant Admistrators and NetworkService full access to the group. This is a dummy group and should be used as a placeholder only. You might want to add a description so that the group is not removed.

Ok so I created that group and it became member of the admin group in AD but I've got no such user as NetworkService there! That's only a local account that is not even in the local Users and groups section on the server.

Anyone having an explanation or step by step guide I'd really appreciate it.

Thank you