Hi nhihoang,
Thank you for reaching Microsoft Community.
For replacements, we do not have an option to just replace the keyboard of the Surface Laptop 3. It will the whole device will be replaced instead but Liquid Damage/Cosmetic Damage is not covered by the Standard Manufacturer's Warranty. If you have the Microsoft Complete Plan (Accidental Damage Protection) for the device, you can use its warranty claim where you'll only pay the deductible amount. Otherwise, a paid out-of-warranty option will be offered. Please see this page for more details: Get service for damaged Surface.
You may also contact support through this page: Contact Us or through our Global Customer Service phone numbers for further assistance.