Generally, you can show a button as a part of an editor, otherwise it is not possible. It can be achieved through implementing custom editor for each platform and insert a button. Here you can find more information, also you can check the code for our Progress Telerik UI for Xamarin app for a reference.
Regards,
Ivaylo Gergov
Telerik by Progress
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Explore the
Telerik Feedback Portal
and vote to affect the priority of the items