Well it depends on a few things.
If a table is provided, then its structure already exists. So in this case if the structures are the same you can do it by a simple : lt_table1[] = lt_table2[].
Otherwise a move correspondgin fields inside a loop should do the work.
If there is no target structure, you sure will need field symbols but we will need more informations also to help you. In the current state, I don't exactly understand what you're waiting for.