As far as I know there is no default method available in iTunes Connect to achieve this functionality. But I've done this in one of my application.
In my application, when each time it opens/becomes active I call a web-service and pass the current app version to it. This service returns a result, something similar to:
{
"version" : 3.7,
"shouldUpdate" : true,
"message" : "Security Improvements......."
}
When I get result like this, I check whether the shouldUpdate
flag is true or not. If it's true I'll show an alert with the server message retrieved above. This alert have only one button and clicking on it, I open the AppStore page of my application (So there is no way user can skip this update).
In my case the code was already there and the force update will work just fine. But in your case, the current app doesn't have any such implementation, so for you it's not possible.