Assumptions:
I assume you have already embedded in UITabBarViewController for your ViewController in Interface Builder. You also have three tab bar items with individual view controllers and created image assets with your icons.
Copy the following code using your current View Controller’s ViewdidLoad method.
self.tabBarController?.tabBar.items?[0].image = UIImage(named: "Icon-1")
self.tabBarController?.tabBar.items?[1].image = UIImage(named: "Icon-2")
self.tabBarController?.tabBar.items?[2].image = UIImage(named: "Icon-3")
Hope it helps,
Thanks & Regards
Mandar Apte