Hey I know its been nearly 2 years since you posted this but I’ve been trying to figure out how to app port and change my address from local to public. I’m pretty sure that the public IP is already setup (I can access my Blynk server without being on my network) but I would like to try those changes. As you can tell, I’m pretty new to this.
Yes, it was an old post… and some things like port addresses have changed since anyhow… so I moved your issue into your own Topic as is prefered 
You issue is really a networking one, not Blynk specific, and how it is done is dependent on your router and your abilities…
Local Server is an advanced option, not recommended for new users, but anyways …
If you can already access your Local Server from outside your network, then what is it you need to do otherwise?.. and why?
Hmmm… OK, are you saying that you need to change your App connection from Cloud to Local server?? if you haven’t already done that, then how do you know you can access your Local Server from “outside”?? Confusing 
Click here to see how to set your App.
https://github.com/blynkkk/blynk-server#app-and-sketch-changes