At an angle, carefully insert a putty knife about 1/8 inch into the seam between the two opening tools.

There are thin metal rails running along the inside of the rear panel, so take great care when inserting the putty knife.

Once the putty knife has cleared the lip of the rear panel, pivot the putty knife so that it is vertical, and carefully (but firmly) wiggle it straight down into the gap between the opening tools.