Steps to view/check carry forward leave balance and expiry date:

1) Enter the "Leave (Pro)" main screen. Then, tap on the "Balance & Transaction".

2) On the "Leave Balance" screen, for those leave type with carry forward, you will see an extra row stated, "Carry Forward" with its balance. An expiry date is shown below the balance.

The carry forward balance would be burnt after the expiring date. And you cannot use it anymore.