in message
I downloaded my emails from my yahoo account to Outlook using POP3
That's what all POP3 e-mail clients do.
however it didnt say it was going to delete the yahoo copies.
Yes it did. That is the default behavior of POP3. So that is how
POP3 e-mail clients work. If you wanted to leave the messages up on
the server, you should have reviewed the program's options, one of
which is to leave messages on server.
Forward them from your local e-mail client back to your mailbox and
thereafter continue using their webmail interface. Have fun.