This cannot be done. The connectors are different in a laptop than in a tower, as well as it's a different form factor entirely. There would be no way to mate the expansion plate to the chassis, even if it would connect to the motherboard, which it won't. Not to mention that laptops can have entirely proprietary designs, meaning that the manufacturer decides on their own form factor without making it a standard.
All of these issues combined makes it impossible to simply take a GPU from a laptop and put it in a desktop. It won't connect, it won't fit in the slot in the chassis, and may be an odd shape that prevents it from fitting properly even if it would connect and fit in the expansion slot, which it won't.