I had a similar requirement. I had saved the username and password in a single file in the form of a key-value pair. Like this
account.details.txt:
username1:password1
username2: password2
You can use something like this:
...
....
....
with open('accountdetailss.txt', 'r') as file:
for details in file:
username, password = details.split(':')
driver.get('https://<your website>')
username_entry= driver.find_element_by_id('Username')
username_entry.send_keys(username)
password_entry = driver.find_element_by_id('Password')
password_entry.send_keys(password)
login_button= driver.find_element_by_id('Submit')
login_button.submit()