Unable to sign into account on Facebook

I have always played on Timelines. I would like to play via Facebook to try out the fleet battle.
This article says that I can sign in via Settings after reaching level 4. https://startrektimelines.zendesk.com/hc/en-us/articles/216746497-How-do-I-play-Star-Trek-Timelines-on-multiple-devices-or-Facebook-
However, the button to switch accounts which features on my mobile version is entirely missing from the Facebook Settings:
This article says that I can sign in via Settings after reaching level 4. https://startrektimelines.zendesk.com/hc/en-us/articles/216746497-How-do-I-play-Star-Trek-Timelines-on-multiple-devices-or-Facebook-
However, the button to switch accounts which features on my mobile version is entirely missing from the Facebook Settings:

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Fleet Boss Battles is not live yet, not even on Facebook
To be able to play your mobile account on Facebook, you must first link your Facebook profile to that account, on your mobile device. That's the last part of that article - it could use some edits to make it more clear.