How to migrate Security user's permissions

Hello,

I have an old NS350
that belong let's say to x.com, and I'm replicating all the FS to a new VNX5300
that I configured to new DNS let's say y.com.
So now I have all the
fs updates on the VNX5300 and i want to connect them to a CIFS server that
belongs to y.com.
How can i migrate all
the user's permissions to the new DNS?