My settings app has been deleted and can

Use App Library to search the Settings app, see -> Organize the Home Screen and App Library on your iPhone

Organize the Home Screen and App Library on your iPhone - Apple Support           

• If you have find the Settings app, tap & hold on the app, then drag to the Home screen & drop it.

If you're sure that its icon hasn't been accidentally moved to a different screen page or into a folder, you can drag and drop it from your App Library (generally it is in Utility folder) to your home page (or wherever you want).

See this support article about that:--> Organize the Home Screen and App Library on your iPhone - Apple Support

Regards

Giulio