Quit the app completely and restart the iPad. Sometimes just closing the app completely and relaunching it will fix this.
Go to the home screen first by tapping the home button. Double tap the home button and the task bar will appear with all of your recent/open apps displayed at the bottom. Tap and hold down on any app icon until it begins to wiggle. Tap the minus sign in the upper left corner of the app that you want to close. Tap the home button or anywhere above the task bar. Restart the iPad.
Restart the iPad by holding down on the sleep button until the red slider appears and then slide to shut off. To power up hold the sleep button until the Apple logo appears and let go of the button.
You can try this as well. Reboot the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons.If those things don't work for you, delete the app and download it again. Tap and hold down on the app icon until it wiggles and then tap the X on the icon to delete the app. Tap the home button to stop all of the apps from wiggling. Go to the purchased tab of the App Store, find the app and download it again.