Do you mean these 3 forums are in different tables and/or databases?
I suppose this could be just a precise manual task. Manually, you would need to adjust forum IDs in _forums, _posts, _topics table so they all are different. Later dump these tables and import them in the database you want.
If you also would like to merge users tables, you should do something the same - update user IDs so they don't repeat, then export/import the dump. |