Export your public key:
keybase pgp export > keybase-public.key
Export your private key:
keybase pgp export --secret > keybase-private.key
Let's import and edit:
gpg --allow-secret-key-import --import keybase-private.key
gpg --import keybase-public.key
gpg --edit-key [email protected]
Inside the gnupg shell:
gpg> adduid
Real name: YOUR NAME
Email address: [email protected]
Comment: <just left empty, hit enter>
Out of the gnupg shell, update your keybase account with the new public key:
keybase pgp update
Check your new public key: keybase pgp export
Update your github or whatever accounts you need to recognize the new email as "verified".