I am able to open the link, which you shared
What is the issue, if you forget the password, please go to https://developer.servicenow.com/
and login with the creds from where you got this instance and there you will get the username and passowrd under manage instance password
If my answer solved your issue, please mark my answer as ✅ Correct & 👍Helpful based on the Impact.
check on the upper right corner, where you find your name like below
You need to click on it
