If you're having problems with a third-party app, issue with that app are completely up to the developer. Apple can do nothing to correct any such problems. You can provide a review in the App Store if you wish to alert other users, but Apple is unlikely to remove the app unless it somehow violates their developer terms of use.
As to removing the files, the only way to do that, unless the app stores the files in the Files folder or on iCloud Drive or other cloud-based service, is either within the app or by removing the app entirely. Removing it and reinstalling, by the way, may fix the crashing problems, though if the app hasn't been updated in a long time, it may well just not be compatible with the current version of iPadOS.
Regards.