Do nothing translates to using the pass
keyword to fill an otherwise empty block (which is not allowed). See the official documentation for more information.
def anti_vowel(text):
new_string = ""
vowels = "aeiou"
for letter in text:
for vowel in vowels:
if (lower(letter) == vowel):
#do nothing
pass
else:
#append letter to the new string
new_string += letter
return new_string