You can get access to a Facebook Page either by being invited to it directly, via Facebook.com, or by getting access through Facebook's Business Manager.
Follow the instructions below to get it set up, either route should work:
Follow these steps to give someone access to a Facebook Page through the new Pages experience:
Go to the Page you want to manage.
Click "Manage," then click "Page Access."
Next to "People with Facebook access," click "Add New."
Type the name or email address of the person you want to give access to, then click their name.
Choose between giving the person "Facebook access with full control" or "Facebook access with partial control."
For partial control: Scroll down, then click "Give Access."
For full control: Scroll down, click the checkbox to allow full control, then click "Give Access."
Enter your Facebook password, then click "Confirm."
The person will receive an email to accept your invitation to access your Page.
Make sure you receive access to edit "Ads", and "Content" at the very least.
Read more here:
Getting Facebook Page access via your Business Manager
Here's a step-by-step guide to request access to a Facebook Page from your Business Manager:
Ensure you have added a primary Page to your Business Manager. Learn how to add a primary Page or change your primary Page in Business Manager.
Go to "Business Settings."
Below "Accounts," click "Pages."
Click the blue "Add" dropdown button.
Select "Request Access to a Page."
Enter the Facebook Page name or URL.
Use the toggles to choose the permissions you need.
Click "Request Access."
Your request will be sent to the Page admin or the Business Manager admin that owns the Page. Once approved, the Page will appear in your Business Manager.
Read more here: