Unable to find App Store on my iPhone

If not in the App Library, then check Screen Time at Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases (or App Installations & Purchases) > Installing Apps, and make sure it is set to Allow.

It's probably hiding.

Keep swiping Left on the home screen until you see the App Library screen

Check to see if the App Store is there. If yes, you can drag it back to the location that you want.

Otherwise, type App Store in the search box to download the app again