Open your code you downloaded from codecanyon in VS Code editor. There is a file called firebase_config.js
Replace the values in the file with the connection string from your firebase project. First you need to create new Web App there.
To change the app name, id, slug etc.. open the file app.json. There, change the name, description slug, desired package name of your app.
To change the app icon and splash screen open the folder assets. There in the folder icons and images change the images with your app brand images. For icon, use square image.