Replacing the keyboard on a MacBook Pro (16-inch) 2019 model is a complex and intricate process that requires technical expertise and specialized tools. Here’s a general outline of the steps involved:

1. **Prepare your workspace**: Find a clean, well-lit area to work and gather all necessary tools and replacement parts. You’ll need a compatible replacement keyboard, screwdrivers (Phillips and possibly Tri-wing or Pentalobe), prying tools, and possibly tweezers.

2. **Safety first**: Ensure your MacBook Pro is powered off and disconnected from any power source. It’s also a good idea to use an anti-static mat and wrist strap to prevent damage from static electricity.

3. **Remove the bottom case**: Turn your MacBook Pro over and remove the screws securing the bottom case. Keep track of the screws and their placements, as they may vary in size and length.

4. **Disconnect the battery**: Locate the battery connector on the logic board and carefully disconnect it. This is crucial to prevent any accidental electrical damage during the keyboard replacement process.

5. **Remove the old keyboard**: The keyboard is typically integrated into the top case assembly, which means you’ll need to remove the entire top case. This involves disconnecting various cables, removing screws, and carefully prying up the top case assembly from the chassis.

6. **Install the new keyboard**: Once you have access to the underside of the top case assembly, you can detach the old keyboard and install the new one. Be sure to properly align the keyboard and connect any necessary cables.

7. **Reassemble your MacBook Pro**: Put the top case assembly back into place, reconnect any cables, and secure it with screws. Don’t forget to reconnect the battery.

8. **Test for functionality**: After replacing the keyboard, power on your MacBook Pro and test the keys to ensure they’re functioning correctly. Check for any issues such as keys sticking or not registering.

If you’re uncomfortable performing the keyboard replacement yourself, or if your MacBook Pro is still under warranty or AppleCare, it’s best to contact Apple Support or visit an Apple Authorized Service Provider for assistance. They can help you with the keyboard replacement and ensure it’s done safely and correctly. Additionally, replacing the keyboard on newer MacBook models often involves replacing the entire top case assembly, which can be costly.