How to forward existing outlook emails to another account?

So I want to forward some of the emails on my outlook (/hotmail) account to my gmail account. I can't forward them individually because emails in question are too many (likely in thousands) and the process would take me weeks. I tried setting up a rule but it's not forwarding any of the mails. Could this be because rules don't apply to existing messages? if so, is there another way to forward the emails that doesn't involve individually forwarding them? Thank you