With over 2 billion monthly active users, Facebook has become one of the most important places for businesses to attract new prospective customers. Needless to say, you as a business owner, would like to engage your Facebook visitors with valuable and interesting content that could potentially motivate them to buy.

With a business Facebook page, you can manage your business information efficiently and can post information relevant to your prospective customers. After you have an admin role for a page, you can also manage reviews and post responses to the reviews. To create a Facebook page, read this help center article: How do I create a Facebook business page?

Claim an unmanaged Facebook page

If you want to claim ownership of an unmanaged Facebook page, you can request to claim the page and can become the page admin. If the page is unmanaged, you will see an 'Unofficial Page' tag under its cover photo.

To claim or merge an unmanaged page, navigate to the desired page and click on 'Is this your business' below the page's cover photo. You will be asked to verify your business phone number, email, and documents in the next steps.

Claim Facebook page with an admin

If the admin already exists for your Facebook page, Facebook recommends that you should reach out to the page admin, as Facebook doesn't settle disputes pertaining to admin roles for a Facebook page. If you cannot contact the admin or the Facebook page doesn't have an admin, you will need to create a new page. 

Sources: https://www.facebook.com/business/help/community/question/?id=155963088162543
https://www.facebook.com/business/help/community/question/?id=10153223380465440