dream face" app not available in App Store in Nigeria

Each app developer decides where to license their products. If the app you want is not available in your country, there's nothing we can do to help you. You could try reaching out to the app developer and let them know that you would like to use their app in your country.

How to contact an app developer - Apple Support

Developers are responsible for choosing the App Stores in which they offer their apps.

This developer, for whatever reason, appears to have chosen not to offer the app in the Nigerian store.