Hello Khan,
probably if you don't want to customize RIPng you just need to enable it on interfaces.
see
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-rip.html#wp1038851
in the list of tasks the only mandatory task is that of interface level configuration
May be the router will create the instance automatically:
you should find this in sh run
ipv6 router rip
!
RIPng accepts a name for each instance (it has a process tag like IS-IS not a process number like OSPFv2)
Hope to help
Giuseppe