How to re-download in-app purchase I've done a factory reset of my HTC One S and I re-downloaded the game Angry Birds. I had previously purchased the mighty eagle, and when trying to get it again in-game, it takes me to the play store. Play store shows a dialog "you already own this", I can either click OK or Details.

When I click OK, it just takes me back to the main screen of Angry Birds and it doesn't redownload. When I click Details, it takes me back to Angry Birds with the message "Unfortunately, Play Store has stopped". I can only click OK and what follows is a loading screen from Angry Birds itself that never stops loading.

Looks like a bug. Are there any alternatives to get the mighty eagle back?
To answer your question 'Are there any alternatives to get the mighty eagle back?' Unfortunately not. It's up to app developers to support redownloading of in app content, and it certainly seems that you have found a bug. 

Get in contact with Rovio at http://www.rovio.com/en/about-us/contact  or contact@rovio.com and explain your issue - they will be able to help you further