You will need to (1) review the LLC's operating agreement, if any, and (2) execute an agreement with the Manager that specifies the terms of the Manager's engagement. You should check this operating agreement to see if the operating agreement addresses how managers are to be appointed. You will have to file an updated Statement of Information with the Secretary of State, and if the operating agreement does not address the appointment of managers, then you will have to amend the operating agreement to allow such appointments. Your corporate records will also need to properly reflect these transactions.
The foregoing response is provided for general informational purposes only and is not a solicitation for business. Please retain an attorney if you need specific legal advice. No attorney-client relationship is established until both you and me agree to establish one, and neither transmission of information herein, nor the receipt of such information, constitutes an agreement to establish an attorney-client relationship.
First of all, does your Operating Agreement allow for a non-member to be appointed as a "Manager"? If not then the Operating Agreement would have to be amended to provide for this. You would then adopt a Company Resolution which would (i) refer to the amendment to the Op-Agmt, and (ii) officially appoint the individual as an additional Manager. If no need to amend the Op-Agmt then you would just have the resolution dealing with the appointment of Manager issue.
My answer is not intended to be giving legal advice and this topic can be a complex area where the advice of a licensed attorney in your State should be obtained.
1. Your Operating Agreement probably needs to be amended. (If you don't have an OA, you should prepare one.)
2. You may need to amend the Articles of Organization.
Especially because two of you are to be involved in the LLC and the business, you should retain a business lawyer to help you do things properly.
This information does not constitute legal advice and does not establish an attorney-client relationship.