Which key is it? If it's a computer key, you may need to replace the key (search the internet for keyboard key replacement and buy the complete replacement set, there are specialist sites). The product you choose blows air to remove small pieces of dirt inside a keyboard, which may be enough, but if the key remains stuck, it will have to be replaced. If the keyboard is less than 2 years old, bring it back to the shop for a free repair. If it's a door key with a lock, use WB40.

I use it for my laptop. Keyboard and fan from it. It still works...