How can I get the Facebook apps using ios

iPhone 5s, iOS 12

For your iPhone it is not possible, Facebook requires iOS 13.4 or later.

iOS 12.5.6 is the latest iOS security update for iPhone 5S, it can’t be update to a higher iOS (13 and later).

Yes, most apps require iOS 13 or later.                                

Considering a newer type of iPhone?

Read this before you buy a newer iPhone.