Remote control ID for different DVRs

Hai,
We have 3 DVRs and 3 remote controls also. Now i can control all three DVRs with any of the remote control.

Now I need to set one remote for one DVR, i.e., I dont want to control a DVR with any remote, instead i need to control just with one.
How can I do that?
DVR model: DS-7216HQHI-SH

Thanks in advance.