Back button is not showing up on navigation header

I want to integrate a third party chat SDK and they don't have React Native support. It's my first time working with Native Modules and from what I've seen I can only derive from NSObject to expose my swift module to obj C then that gets exposed to React Native side.

Right now, I have this native module code snippet in swift:

@objc
@IBAction func showAnswerBot() {
        do {
            let answerBotEngine = try AnswerBotEngine.engine()
            let supportEngine = try SupportEngine.engine()
            let messagingConfiguration = MessagingConfiguration()

            DispatchQueue.main.async {
                if let viewController = try? Messaging.instance.buildUI(engines: [answerBotEngine, supportEngine],
                                                                        configs: [messagingConfiguration]) {
                    let nvc = UINavigationController(rootViewController: viewController)

                    nvc.navigationItem.leftBarButtonItem = UIBarButtonItem(title: "back", style: .plain, target: self, action: "backAction")

                    UIApplication.shared.keyWindow?.rootViewController?.present(nvc, animated: true, completion: nil)
                }
            }

        } catch {
            // do something with error
        }
    }

    @objc
    @IBAction func backAction() -> Void {        
            UIApplication.shared.keyWindow?.rootViewController?.dismiss(animated: true)
    }

Here is my interface for objc code:

#import <React/RCTBridgeModule.h>

@interface RCT_EXTERN_MODULE(ZendeskMessagingChatModule, NSObject)

RCT_EXTERN_METHOD(showAnswerBot)

@end

Right now "this works" in that it exposes the chat window as a modal window in my app but the user can't go back or cancel the chat/close the window even though I set the backbutton on the navigation item. I want to add the cancel button at the top but I'm not sure what I'm doing wrong here?

What am I missing above?

Thanks!