Hi Nayab,
If your other shelves are multipath connected, just remove te last cable from the last shelf.
Do this loop for loop(connections to the A IOM and B IOM).
You'll see that your disks will be connected through a single path during the activities.
Add the shelf and connect it the same way the other shelf was connected.
Example: cable from your controller port goes to the B IOM from shelf 2, disconnect this cable from the shelf.
Connect then from that port a cable to the new shelf (also to the B IOM) but on the input port.
If the controller will recognize the new disks(can take a few seconds), repeat this for the A IOM.
Here's a link that maybe give your more information: https://library.netapp.com/ecmdocs/ECMP1119629/html/GUID-7272C432-F8FC-4598-BF88-D36173442BD3.html
Regards,
Arco