Since the connection activities on for iOS are full automatically managed, there's no way to force the connection to the server but the application restart.

How to restart the application on iOS (you have to send the application in background by pressing Home button on the device: it's the only physic button on the front panel)

1. Double-click the Home button to see your most recently used apps. (fig. 1)
2. Swipe right or left to find  app that you want to close. 
3. Swipe up on  app's preview to close the app. (fig. 2)
4. Now you can start the application a usual by clicking on icon

fig. 1	fig. 2