How do I replace a broken key on a logitech keyboard for iPad?

Easiest way is to contact the manufacturer, otherwise keys for Cherry MX switches are generally interchangeable as well as most laptop keys as the mechanisms are the same.

Often the keys wont match perfectly if you steel them from another product but it works.

My "R" came of and I do not know how to put it back on. My iPad keyboard is a amazon keyboard. Does this mean that my keyboard is broken or will I still be able to fix it? I will be waiting for an answer. Hope you understand. Thank you.

Spare keys for some of the Logitech keyboards are available but not from Logitech which is a pity. It does not help when people and even suppliers bother to define the exact keyboard model!