Before you start you'll need to make sure you have either the page name or the URL of the Facebook page to hand.
> Step 1
Go to https://business.facebook.com/settings and select your business
> Step 2
In the left hand navigation, select Pages:
> Step 3
Once in the pages section, click the blue Add button:
> Step 4
In the dropdown menu, select Request Access to a Page:
> Step 5
Enter the page name or URL and select it in the dropdown:
> Step 6
On the following dropdown, select the level of access you require. Standard access will give you the ability to publish and post as the page, whilst Admin access will give you a higher permission level and allow you to do things such as manage lead forms and conversion pixels.
> Step 7
Once you've selected your access level, click Request Access. The page owner and admins will then receive a notification in Facebook asking them to review and accept the request.
> Step 8
Once permission has been granted for your business, you will then need to allocate people from your business to have permission to run ad campaigns on that page's behalf. From the Pages tab, click the relevant page, and then Click Add People.
> Step 9
In the resulting pop-up, select the individual from your business that you want to give permission, select their access level, then click Assign.
If you need to request access to a large number of pages, use the Request Access to Multiple Pages option in step 6. This will allow you to use a spreadsheet to upload pages in bulk, however you need to know the Page IDs in order to use this method.