help please

Hi there
I have a canon 5d3 and have been using wireless flash triggers - yongnuo 603II. Trouble is that the transmitter is now stuck on the camera!

I read online that there is a 'locking pin' that must be stuck - does anyone have any suggestions how to "unlock" it?

Is it expensive to send to canon to repair (I am in the UK) or should i just take the trigger apart and try to do it myself -may be cheaper unless I damage the camera in the process?

Any help appreciated

Best
Tony