Also, you could try signing out from the App Store, then restarting the device and signing back in.
To sign out, go to the
Features tab in the App Store, then scroll down and click on your Apple ID. Choose
Sign Out when prompted, then restart your device and sign back in.
And if you're not sure how to restart your device, here is a link with the steps and an image:
https://support.apple.com/en-us/HT201559