The first thing I am going to have you do is exit OnDeck and kill any processes associated with it. If you are not familiar with ending processes there are different methods depending on what type of device you are using.

If you are using an iPhone/Pad/etc double-tap your the home button and a small bar will appear across the bottom of your screen. Touch and hold any OnDeck icons in this bar until a minus sign appears on the corner of the logo, press the minus sign to kill the process. 

If you are using an Android device the steps needed may vary slightly based on the the specific model/software. But as a general guide you will need to go to your home screen, press the menu button and go to  Settings > Applications >  Runnings Services. Tap any OnDeck services that are running and stop them. 

After ending all the OnDeck processes uninstall OnDeck from your device. Please note that when uninstalling you will lose any un-synced information, make sure to copy any necessary information. Once the uninstall has completed re-install OnDeck from the App Store/Google Play