How do I write a new row in a csv file with python(editing the csv)

Question

with open('usernamesandpasswords.csv', 'w', newline='') as f:
    writer = csv.writer(f)

    writer.writerow(['User ID', '', '', 'Password'])
    writer.writerow([user_Id, '', '', password_for_user])
    f.close()
     

#I want to add a new line to this to allow for more user ids and passwords to be able to be added to the list, while keeping the original data. How do I do this?