In debug mode you can click on your branch link (maybe you can copy this link on a notes page or send it to yourself on whatsapp) and it will open the link on safari and redirect you to appstore (Don't install the current app from appstore).
Post this you can simply run the app on your device connected to your system via xcode. This will have the same effect as a deferred deeplink. (you can debug this in your app delegate, just make sure you are on the same network.. wifi or 4g as branch uses this for fingerprinting and might not run the deferred deeplink if this changes between the time you clicked on the link and launched the app via xcode.)
If you wan't to test as to how it will behave in production enviornment you can use test flight for the same. (Click on link and once it opens in safari install the app via test flight)