Change values of a particular column to value_count()
Try this:

# Do value_count outside of loop to avoid doing it multiple times
vc_item1 = data['Item 1'].value_counts()

data['Item 1'].apply(lambda x: vc_item1[x])


But if understand your comment correctly you want both key and value in each cell:

vc = data['Item 1'].value_counts()

data['Item 1'].apply(lambda x: str(x) + ':' + str(vc[(x)]))