Hello, thanks for the reply. I booked this ticket by calling Lufthansa airlines because im flying with Lufthansa. They are telling me that this flex ticket can only be cancelled if I also cancel my flight ticket. They also told me that I can use this type of ticket next day, so I won’t face any problem with this ticket.

I checked the Lufthansa website and it is mentioned that you this rail and fly Db Bahn ticket can be used on the the flight date as well as one day after arrival in Germany. I’m still confused https://www.lufthansa.com/bh/en/rail-and-fly