Most client's only need to import from one Xero account but if you are consolidating or need to import from two accounts for whatever reason it can be done.
After you have run the first Xero import, you may have trouble trying to run another from another account. enableHR will assume that you'd like to import again from the account you've selected initially.
To remedy this, delete your history and restart your browser. When you try again to run a new Xero import, it will no longer have your initial Xero import set and you will be able to run another import from a new account.
You may also check the "How to unlink Xero Integration" section of the Xero Employee Import knowledge base article for more information.