Here are some steps to help you fix your laptop key:

1. Clean Around The Key. Clean around the missing key with an anti-static brush or a toothbrush. This helps remove dirt and other debris that may be inhibiting your laptop's ability to recognize the key.
2. Check Your Keyboard Layout. Seeing as you've lost a key, make sure you double-check your keyboard layout. This will help you locate the exact positioning for the new key.
3. Purchase The New Key. After you've determined the exact positioning for the new key, you'll have to purchase a compatible replacement. Ensure that the replacement key corresponds with your laptop's model number.
4. Install The New Key. Install the new key and ensure it is secure. Most laptop keys use a small plastic scissor switch and a metal guide bar to secure the key – first insert the guide bar, then the plastic switch.