Hi Syed,
The built in database viewer is used when developing so it should become available when you run your project locally. If you are trying to change your data in a cloud environment, then I recommend using a microflow to update it.
Here the documentation on how to start the built-in database viewer:
The 1st requirement is to run your app locally!
Built in Database viewer is available when you run your application
Built in Database viewer is available when you run your application