I found this information very interesting as I'm sure a lot of you that OWN the HK-91 or clone will as well.
Since I was limited to 4 pics The ones below are the ones I chose. But there are more at the link below that attempt to give more of an explanation of how this procedure is done.
How to disassemble the G3 rifle for cleaning in 8 easy steps.
How to reassemble the G3 rifle after cleaning in 11 easy steps.
Detail of locking piece ref. step 2 in assembly manual.
Detail of bolt carrier ref. step 2 in assembly manual.