Greetings from GoVacuum,
The reset buttons on the Riccar vacuum cleaners are located at the bottom of the vacuum cleaner in the back, underneath of where the wand sits on the vacuum cleaner.
Here's a picture of a Riccar 8925 which replaced your 8850 a few years ago, but the reset switch will be in the same exact location on all Riccar uprights;
Here's a closer look of the reset switch;
I hope that I was able to answer your question. You can avoid the reset switch flipping in the first place by always ensuring that you change the bags frequently and when full, as well as the motor filter that sits underneath of the bag. Also keeping the vacuum from clogging will prevent this.
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