Removed the wall oven to access temp probe connector strapped to the back of the oven. removed 2 screws holding probe inside the oven & replaced. Searched for the "fixing kit" thermostat part I was suggested to replace along with the probe. No thermostat type part was found in my oven, even though Bosch says it fits "somewhere". Reinstalled the wall oven & tested. The temperature is working normal now. Will return the fixing kit.
I lifted up the microwave ceramic dish and put it on countertop. Lifted out old roller ring and replaced with new one. This took 10 seconds. Carefully placed ceramic microwave dish back atop roller ring and aligned its center over stationary part that rose from bottom center of oven. This keeps ceramic plate in place as it revolves. I canceled pending service call from local appliance repair service and saved $99.