is it in you itunes library if yes install appsync, then select it and sync.
how did you initally get it on the pod. If you installed it straight onto the pod (not itunes) you may need to select transfer purchased apps in itunes (right click your device in itunes and select transfer apps you will still need appsync on the pod}
I used insta not app store, i have just tried transfer purchased apps but no still not there ???