Welcome to Robotics, Poyraz Sagtekin. Is your problem just that you can't assign IDs to the motor or is it that you can't communicate to the servos at all?
What IDs have you given to the other servos? There is a guide here that says, in part:
Before you set your servo IDs, here are some things to keep in mind.
- You can only ID one servo at a time. Do not plug multiple servos into the ArbotiX when using the DYNAManger.
- Make sure you label your servos as you ID them! This will make the assmebly phase go much faster
- All servos come pre-set to ID # 1. However we still recomend that you use the DynaManager to set the ID on servo #1. This will make sure the servo's baud rate is set correctly, as well as allow you test the servo.
- Most kits use only AX-12A or AX-18A servos. For these kits, you can simply ID the servos in sequential, increasing order for however many servos you have. The exceptions are:
- If you have a PhantomX Reactor Robot Arm without wrist-rotate then skip servo 7 (ID the first 6 servos normally, then set the last servo to ID #8)
- If you have a WidowX Robot Arm MK-II, see this diagram. (The MK-I diagram is availbe here)
The things I would ask you to verify are that:
- You're only trying to setup one servo at a time,
- The servo is plugged into the correct port (view the image on the instructions of how to connect), and
- That you've set the IDs on the other servos correctly. It looks like the MX-64 servos should be set to IDs 2 and 3.
If you do this and you're still having trouble, please edit your question to include what exactly the problem is - if you're getting an error, what the error is (verbatim), how you're connecting it, how you're powering it, etc.