tacettin

This is quite a 'classic' problem and the immediate thought ("just do it mySQL") doesn't work here because of the need to have the rails piece that encodes a password that is entered.
So you need to actually use rails, something like this (this should all be happening in your local development environment which is the default when working locally):

You need to create a user.

Try this:

cd the_root_of_the_project

script/rails console