how to do this mysql task?

I have a table called survey_results_BC_temp. It has the following fields:
https://photos.google.com/photo/AF1QipMu...fpv9sCqWeM
I am trying to update the number_of_employees column. I have tried this:
UPDATE survey_results_BC_temp set number_of_employees=COUNT(distinct user_email) WHERE item=(SELECT item FROM survey_results_BC_temp)
But it doesn't work. 
Then I tried:
https://photos.google.com/photo/AF1QipMd...6Te7ruC9An

How can I fill in the number_of_employees field?

proof that an old dog can learn new tricks