1. Remove the black plastic casing on the lid,
2. Turn the lid upside down and remove the nut in the centre on the lid,
3. Turn the lid back over and the handle can then be lifted off,
4. Here you will see to the right hand side a section with what looks like teeth. This piece has probably come away and needs pushing back on,
5. Then place handle back on lid, and tighten the centre nut again,
6. The lid will now open and close again.