You used the for loop wrong.
your function is acting on the argument/ list called x
and what you want is for each piece of data in the list x, if the piece of data is equal to the string 'fizz', add 1 to the amount of times fizz has been counted
so it would look like:
for piece_of_data in x:
if piece_of_data == 'fizz':
count += 1 #the correct shorthand for adding something to a variable is +=
try that and tell e how it works,.... also, replace piece_of_data to the word item