Thank you for your reply rocks1, I appreciate it.
I realise I wasn't specific enough. It's not the actual arm that has fallen off, that's actually still attached to the structure:...it's the bit that attaches to the back (that the arm attaches to) - where there are two holes. At the back...
After opening the door on our dishwasher we realised that the upper arm has fallen off; we can't se how to reconnect it. We cannot see any part that has become lose but cannot just the arm back to where it has come from. Can anybody help please?