If you want to migrate backup or archivelog files from asm disks to local disk, you can use below command. But you have to create a directory to migrate backup and this directory owner have to be grid user.
Copy File Command
[grid ~]# asmcmd
ASMCMD> cd FRA/backups
ASMCMD> cp mynewbackupname.bck /localdiskpath/mybackup.bck