Hi Sunil,
Could you please let us know, whether both the internal tables are having same structure?
In case both the internal tables are same structure(same number and type of fields including same field names) - the we can use tab2[] = tab1[] as suggested by Tanka and Sander.
If both are not having same structure,then please share the both the structures of internal tables, so that it would be easy for us to help you in better way.
Thanks