The default Firebase app already exists

[luisanm333]

I have never use Firestore nor Firebase.
When I run the project it shows this message:

"The default Firebase app already exists. This means you called initialize_app() more than once without providing an app name as the second argument. In most cases you only need to call initialize_app() once. But if you do want to initialize multiple apps, pass a second argument to initialize_app() to give each app a unique name"

Would you help me, please?