To reattach a laptop key that has popped off, follow these steps:

1. Check the laptop key and its slot to ensure they're clean
2. Determine if there's a plastic, metal, or rubber scissor-slot holding the laptop key in place
3. If you are confident you can properly reattach the laptop key, slowly and carefully pop it back onto the slot
4. If it won't stay in place, use an old credit card to press the key firmly into the slot
5. Test the key reattachment is complete by pressing the key down and checking if it functions properly