Create a function to iterate through an array in swift

I'm trying to create a function in Xcode that I can call every time I hit a button to iterate through an array in sequence which then updates the value of the button title.

I can't seem to crack the challenge. I've tried various iterations of while loops and if statements but everytime I run it I end straight up at the last value in the array. Here's the code I've got at the moment, I tried to add a break clause to stop the function from automatically iterating through the whole array but it's now throwing up an error message saying that the code after the return statement will never be executed:

var repArray = [1,2,3,4,5]
var repArrayIndex: Int = 0

func repCount () -> String {
    if repArrayIndex < repArray.count {
        while repArrayIndex < repArray.count {
            return "\(repArray[repArrayIndex])"
            break
        }
        repArrayIndex++
    } else {
        return "\(repArray[0])"
    }
}

Any ideas?