If I understand you correctly deco20, you had 3 accounts on your old machine but now you want to transfer only one of them to your new machine. I would do it this way.
1. Make sure you have the same user account name on your new and old machines for the account from the old one you want to keep.
2. Log into the new machine under *another* account and use MA. It will recognise that there's an identical user name on the old and new machines and ask you if you want to bring that account over to the new machine.
3. Once you've done that, and checked it, you can delete the unnecessary accounts on the new machine.