How to use a function with return inside another function with return in Swift

Question

I am trying to make my function to read data from Firebase Storage taking image reference as an input and getting UIImage in return.

It gives me error: Cannot convert return expression of type 'StorageDownloadTask' to return type 'UIImage'

As I see, the problem is that Firebase function already has a return and it conflicts with my function. As a solution, I have tried to make the function return several values but with no success.

Is there any way to solve this issue? I would really appreciate any help.

func convertImage(imageRef: String) -> UIImage {

    storage.reference().child("images").child(imageRef).getData(maxSize: 2 * 2048 * 2048) { data, error in
        var image = UIImage(named: "empty_plate")
        if let error = error {
            print(error)
        } else {
            image = UIImage(data: data!)
        }
        return image
    }
}