Not able to remove debit card which is already added wanted to add new one

This may be because of the fact that you have a recurring subscription. You might need to cancel your subscription before you remove your card, but that’s not convenient. If that’s the case they would tell you before you try to remove it, so it might be that there is a payment that’ hasn’t not gotten through yet, in which case you would either need to wait, or look at the following. You are able to have more than one payment method. You can set up your second card onto tourbillon device, I presume, and then once it is successfully synced to your account/device, you can remove it. All of this depends on if you mean your iTunes/App Store payment method.