iCloud email account in Outlook on my iPhone

I use Outlook on my iPhone and have set up two email accounts on it, my Apple account and my Microsoft account.

I had to use my Apple ID and an app-specific password for the iCloud account, but this means I'm using my iCloud email address, which I'd prefer not to.

Where, in the settings for the app, can I change the email address I want to use, please?

I can do it in Outlook on my iMac easily enough, but I can't see how to do it, even though it was that way before I had to restore the phone's OS.

Thank you.