You are not telling enough for us to help you. The minimum information required includes the course you're trying to attend, but sometimes also the exercise (chapter, title, etc.).
Luckily though, if you carefully examine the information given to you in the exercise text, there is always information about the credentials you need to use to be able to log in.
In the first practical lab exercise in the course, the course authors generally give instructions to the machines. For RH124, it would be this exercise:
Generally, we provide credentials either in the front-matter for the course or in this first practical exercise, RH124 is a bit special because you start off as an unpriviledged user and later, log in as root, so the credentials are provided as the course progresses. I think this is the only course that operates this way.
Usually, we keep a lot of the credentials the same across classes, there are a few outliers to that, but in the last few years we've tightened up our standards for these credentials.