As far as I know, there is no way to rotate a UITabBarController on its side. However, you could take a UITabView (https://developer.apple.com/documentation/uikit/uitabbar) and rotate it on its side using Core Animation. To add functionality, set something as the UITabBar's delegate to learn about changes.
As far as an actual code snippet, I typically write in Swift, but I found another Stack Overflow answer with what you're looking for.
How to programmatically rotate image by 90 Degrees in iPhone?
Hope that helps, have a nice day!