When linking Facebook, if the wrong account shows for 'Continue As', the below describes the steps to log out of that account so you can proceed with the correct account.

Please open the internet browser on the device to confirm that Facebook has been logged out. Then return back to the link to connect Facebook. From there, if successful, the user should then see a Facebook login screen. Continue by logging into the correct account. 

If using an iPhone, you may need to clear the cached images and cookies for the Safari. 

Step 1: Go to Settings > Safari. Scroll down and tap Clear History and Website Data, then tap Clear History and Data.

Step 2: Next go to Settings > Safari. When in the Safari Settings menu, scroll down to the bottom and tap Advanced > Website Data. Lastly, tap Remove All Website Data and then Remove Now.

Note: This clears your Safari cache on iPhone. Remember, this will get rid of website data, browsing history, and website cookies. Alternatively, a user may just clear Facebook from the browser history, rather than clearing all of Safari. For more information regarding Safari setting click here to Apples Support - Safari User Guide - HERE