How do I access lost previous opened e-mails that were with my Yahoo e-mail but is gone after switching to pop?

I just changed e-mail service from regular Yahoo -e-mail to popmail. That was completed successfully. However, all the previos mail I had under the normal e-mail is gone. I did see it download but can't find it.. How do I access my previous e-mails people sent me...How do I access lost previous opened e-mails that were with my Yahoo e-mail but is gone after switching to pop?searching from the sender

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