How to add blog functionality to an existing strapi app?

I am wondering to add blog functionality to an existing strapi app. I have folowed this tutorial Strapi - Build a Blog Using Strapi and Next.js which is worked well for creating a new app & seeding the database with sqllite.

How can these collection types be added to an existing app?
Also how can we obtain a script to create the database structure like creating the tables? there is a file that seeds this database but I am unclear how to view the file which creates the database.

Thank you in advance for any & all information.

System Information
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