On-screen keyboard on newer iOS phones?

How in the world do you pull up the on-screen keyboard on newer iOS with the OnlyKey duo plugged in?

I have searched online and have found no solutions. This is quite an oversight and very frustrating. I just recommended these to my boss as I have been very happy with them, but I have an Android. He just bought two of them, and I would hate to tell him that there is no solution. Please help!