Are you just providing a link to the instructions, or do you still need a question answered?
If you are still asking about remote access...to enable remote access by default, you need to compile a custom firmware image that has a firewall rule - permitting WAN access by default. Please note, this is dangerous.
I know but what are the steps to compile a custom firmware to the router mentioned ?
In particular, pay attention on how to install files, as, by default, password-less root logins are enabled on a "clean" flash. Note also the password encryption types supported, as they are significantly reduced compared to "desktop Linux" and can't be extended, due to limitations of the C libraries in use.
is there any specifically guide ? not in general