Are you using the Apple "Mail" app or the Fastmail app?
The Fastmail app icon looks like this:
https://itunes.apple.com/us/app/fast...ts/id931370077
The icon you use to start the Fastmail app looks like the big icon on that page (the envelope with a yellow wave). If you don't see Mail in the upper left corner, touch the left arrow in the upper left. Once you see Mail you touch it to see the menus I listed below (including Contacts).
Fastmail is changing their iOS app to a new user interface (which is now in beta). With the new app you will see Mail / Contacts / Calendar / Notes / ... More at the bottom of the screen (instead of the Mail button in the upper left used by the old iOS app).
The Apple Mail app icon looks like this:
https://upload.wikimedia.org/wikipedia/commons/thumb/5/52/Mail_iOS.svg/1024px-Mail_iOS.svg.png
If you are using the Apple Mail app, you will need to use the separate iOS "Contacts" app to edit your contacts. The Contacts icon looks like this:
https://www.briomedia.co.uk/wp-conte...-1032x1031.png
Bill