have a button outside the collection view to do what the collection view cell is supposed to do

I have a collection view acting as image carousel when i press on the cell a pdf file will open, the code below will do that. what i wanna do is to have a button to press on it instead of pressing on the cell itself. but i dont know how to do that because of that line [login to view URL] = indexPath func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) { [login to view URL] = indexPath [login to view URL](withIdentifier: "showBook", sender: self) } override func prepare(for segue: UIStoryboardSegue, sender: Any?) { if [login to view URL] == "showBook" { let vc = [login to view URL] as! showMo2lfatVC [login to view URL] = [login to view URL][[login to view URL]] } } This is my button function and this is what i have tried @IBAction func openBook(_ sender: Any) { // [login to view URL] = indexPath // [login to view URL](withIdentifier: "showImage", sender: self) // [login to view URL] = indexPath }