storing data in mongodb - want to store as string and not a date

Question

I am using the following code to store information in a document in mongodb:

# Opening JSON file
f = open('quiz.json')

# returns JSON object as
# a dictionary
data = json.load(f)

# Closing file
f.close()

username = data["username"]
first_name = data["first_name"]
last_name = data["last_name"]
password = data["password"]
email = data["spare_1"]
role = "student"
expires = "31-12-2022"

user = User(spare_1=email, username=username, first_name=first_name, 
last_name=last_name, password=password, role=role, expires=expires)
user.save()

The problem I have is that the 'expires' field is uploading to mongodb in the format '2022-12-31T00:00:00.000+00:00' which causes me problems later as some dates uploaded form a csv file are uploading as only "31-12-2022". As it then is storing them differently, later when I go try to:

datet = session['expires']
datet = str(datet)
account_expires = datetime.strptime(datet,"%d-%m-%Y")

I get the error:

ValueError: time data '2022-12-31 00:00:00+00:00' does not match format '%d-%m-%Y'

I don't have enough knowledge to format these dates, so it would be easiest I get the expiry date added as the string "31-12-2002" only? Any help would be appreciated.