First heat the Lil Bratz head to remove it from it’s body

Then cut off the long neck peg spike above the knob

Now remove your Petshop head from it’s tiny body, heat the head and pull out the semicircle neck piece:

Place the semicircle neckpiece over the Lil Bratz neckknob and push it back into the Petshop head.

The head will be a little wobbly but firmly on! The Lil Bratz body is a great match for normal Littlest Petshop heads.