1.4 mpi rear door handle

Thought I was being clever by resurrecting a year 2008 thread yesterday but no replies so have started from scratch.

Have lost /had stolen the small plastic cover forming part of the rear n/s door handle. (On the front doors it would be the keyhole part). Obtained a replacement thinking that it would just clip in but it doesn't so I am wondering if there should be another component such as dummy lock barrel which goes in first to make a secure anchor.

Am reluctant to take off the part on the rear o/s door to see what's what in case I can't then put it back securely and didn't find the Haynes manual to be very helpful.

The att. photos should hopefully clarify.