Most passes can be refunded, though you lose 15% of the value.

The answer can depend on which type of ticket you have.

If you have a 3 month pass then you can activate it on the 4th, not use it for the next 20 days and then use it for the 2 months and 10 days after that.

If you have a 15 day pass, then you aren't going to be able to use it at any time after you arrive on the 24th which is 5 days after your pass validity expires.  Arrive earlier or get a refund and buy a new one which will start later.

If you have an X days in 1 month pass then you need to do the maths and see how your itinerary fits in with the remaining count of valid days and the ultimate expiry of the pass.

You can exchange your Pass for a small exchange fee of 15€. Just make sure the current Pass is not activated and buy a new Pass via our website, log into your account, go to ‘Pass details’ and then ‘Refunds and exchanges’. Select the Pass you wish to request a refund for. An exchange refund will be processed for the old order (100% minus a 15€ exchange fee per Pass). You’ll be able to activate your new Pass up to 11 months after the purchase date. This would make your Pass valid on the desired date.