Your question doesn't make sense, so I am not sure how to answer.
In RAID5 you have your parity spread over all your disks, so if one disk fails you can rebuild with the rest of them. But you can only rebuild if you have another disk of the same size (and best would be same make and model).
In your case (if I understand correctly), one of your three disks (4TB each) died. You now need another disk of 4TB and partition it the same as the other disks.
Here is quick way to copy your partition table over to the new disk from one of the working drives:
I hope that answers your question.