Remove upper and lower baskets for access. Remove 4 Torx screws holding drain/filter assembly, accessing last screw by rotating the water duct clockwise. Be sure to first un-clip the water duct at top and rear of dishwasher so that it can be moved. (Take the opportunity to remove accumulated deposits behind the water duct). Remove the drain/filter assembly and then remove the single screw holding the food chopper housing. Then remove the chopper assembly which is likely to be in pieces if it failed due to a hard object getting lodged inside - such as a screw, piece of plate or glass, etc. Carefully remove ALL debris and I recommend using a shop vac to more easily suction out the water and any debris in the sump. (I strongly recommend using a butter knife or screw driver to pop off the round filter screen as you can then remove LOTS of debris that is choking off water flow to the dishwasher arms, impairing its performance. Cleaning out all the ducts and arms will restore as-new performance!).
Inspect the chopper cover and carefully scrape away any plastic damage caused by sharp objects, if evident. The diameter of new chopper screen is slightly larger on one side. Install the new shopper assembly screen's larger diameter half into the sump groove. (I recall the larger side goes into the sump groove but please double check). The smaller diameter side will go into the groove on the chopper housing. This installation is a little tricky and requires the chopper screen to be sitting vertical to align with the semi-circular groove in the cover. It may take a few attempts before you get it right. It helps to rotate the chopper assembly shaft so that its splined end slips over the black drive shaft in the sump. When you have it right, the chopper housing will be fully seated, only requiring light finger pressure. Note that the cover's grooved leading edge fits over the ridge in the sump housing. Do NOT force the chopper housing cover into place with the screw - it should not draw down the cover as you tighten it. Reverse the