He has an Electrum wallet already on desktop, he can only have 2fa on mobile phone, he can not have both Electrum wallet and 2fa on mobile phone because it is not good to have both the authenticator and the wallet together.
The instructions nc50lc has given will restore a watch only version of his 2FA wallet to his mobile, which will not contain any private keys. It is fine to have both a watch only 2FA wallet and the 2FA app on the same device, since there will still only be access to a single private key via the 2FA app, and no access to any of the private keys via the watch only wallet.