If you can't remember your first device in synchronization passcode, no one can help you get into the group. This is the information only you know. I have checked your group and I can't see first device in the list, which means that you have to removed it by turning off sychronization on it. Try use any master password/password you ever have had set on any of your devices. If it won't help then only reset of your synchronization group can help you to use same account for synchronization again.