If you signed up through Facebook through the app on your phone then you should be able to manage it by going into google Play. Here is a help FAQ on that from Facebook. https://www.facebook.com/help/389356905082923?helpref=faq_content
If you signed up through a web browser on desktop or laptop, you will need to manage it through the same method. Here is a link from Facebook on an FAQ on that how to manage methods - https://www.facebook.com/help/389356905082923?helpref=faq_content
https://www.facebook.com/help/1513879196089826