"Unable to purchase
This item is for an app that was purchased by a different Apple ID.
To buy this item with this Apple ID you must first purchase the app."
I'd try deleting the app and reinstalling it. Hopefully, that will get rid of that error message…
If you want to export any presets or preset lists you've created before doing so, you can do that by clicking on the Settings button in the bottom right hand corner of H9 Control and going to 'Export Presets and / or Preset Lists'.