You cannot install that app on your iPhone.
An iPhone 6/6plus can't be updated beyond 12.5.6, it doesn't have the hardware needed to run anything higher.
If you need a higher iOS version, you will have to purchase a newer phone.
3 replies
So how do I get Facebook app pls ??
You don't. You can use the web version, or buy a newer phone capable of running a newer iOS.
Please how do I update my iPhone 6 without using WiFi???