I'm not sure, here, what you mean by "replacing uname by my user name," because what you're supposed to type is exactly what you see in the instructions: (uname -r). This is so that bash will run the command uname -r with the output of the command, which will be the exact version of the running kernel, which is what you need here. I think that you would need to edit the command line in GRUB, to boot your most recent kernel into single-user mode one time, run dracut again, with the correct arguments and try to reboot normally.