When you pull down the front flap there is a cylindrical white button. Push the button whilst turning the hand wheel towards you. After a couple of turns the tubes will connect and you should be good to go. If it still doesn’t work you will probably have fluff in your tubes and will have to pass a thin wire through the threading port to push it out.
Don’t forget to disconnect the tubes after threading by pushing the chrome lever to the right.
Have you got a manual because if you haven’t I have and I could scan it for you.