Facebook Pages have no usernames and passwords to manage.
How to Access My Business Facebook Page?
Facebook Pages are managed by users that have access to the business page. To access the Facebook page, users need to use their personal Facebook user access to log in.
To see what pages you are managing, please log in to your Facebook account, then visit the link below:
How to View Existing Admins Who Have Access to My Business Facebook Page?
If you see your Business Facebook Page click on it, and from the left sidebar, click on the Settings button.
On the Settings Page from the left sidebar, click on the “Page Roles” tab to see all existing users, or you can add more users when needed.
How To Add An Admin To My Facebook Page?
In order to add a new user, you can use their Facebook ID or email address (unless they have blocked their email under the user Privacy Setting of their Facebook user account).
Users on Facebook may have different roles (authority) to manage content and other users. Make sure to give necessary permission to each user you add to avoid unpleasant outcomes if their account gets hacked, or in the case of most businesses if you fire an employee they may sabotage or harm your business.
Warning! Unless when the Facebook page is owned by a Facebook business account, all admins are able to remove all other users (including admins of the pages and business owner if the business owner is only an admin of the page). So, before giving any admin permission to any user, make sure that the person will not steal your page for any reason (i.e., if the user is a legal company or someone you trust) or you need to create a Business Facebook account formally own the page.
A safer option to give access to Facebook Agencies (companies who want to help you manage the page or run ads) is that they request “Agency Access,” You accept their access and only approve permissions necessary for them to function.
The screenshot below shows an example of proper Facebook Page accesses. The below example Facebook page is owned by a Business Facebook account, agencies have access with restricted permissions, and there are admins on the page for trusted users (owner, employees, or contracted companies).