Problem with downloading old apps

Some years ago I had got 3 apps and I never downloaded them from any device. Some time before that started to happen that every time I open my iTunes its says theres an error saying that those apps are not available to download. I tried to find them in AppStore but they seem to be missing. My question is how can I undo the purchase of those 3 apps in order not having my iTunes trying to find old purchases every time it starts?