var containerViewBottomAnchor: NSLayoutConstraint?

    func setupToolBar() {
       ...
       containerViewBottomAnchor = containerView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
       containerViewBottomAnchor?.isActive = true


    }

    func modify(){
       containerViewBottomAnchor?.constant = -500
    }

containerView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -500).isActive = true