Upvote:5
Yeah, the Regiomove app sucks, but there are alternatives: you can buy KVV tickets through Deutsche Bahn's DB Navigator app, which lets you select an address in a country basically anywhere. And there's also the Fairtiq app, which doesn't require an address at all (note that you have to have location and internet always on for Fairtiq, as it calculates the fare based on actual distance travelled).
If you require further assistance, there's a Baden-Baden public transport customer centre at Augustaplatz.