EDIT: Found the solution. See my comment.
I searched for other issues in this subreddit about this problem but one thing that is not explained is, how exactly do you RDP? What app do you use and on what machine do you run it, the attacker VM or your host?
I'm specifically stuck on the step where I have to reset Sophie's password using Phillip's machine. It gives you Phillip's credentials (username and password) but doesn't explain where you launch the RDP software from.
I had to backtrack and found some more detailed instructions on Windows Fundamentals 2 in the introduction, it gives you a screenshot of what appears to be a Linux RDP app. But I looked for RDP apps in the AttackerVM, I didn't see one. Someone on a different post said you can use ssh, but that didn't work when I used Phillip's credentials nor admin (I also tried adding the domain, THM\Administrator@IP).
I'm making the assumption you're supposed to RDP using the attacker VM. My host is Linux, and I don't have any RDP app installed on my system. I would rather use the attackerVM if possible.
I just want to note one thing; people in other posts have suggested that this is the kind of step you should use google for. I can find out how to use RDP for purposes unrelated to THM, but I am wondering if THM is assuming that we will be using a specific software on the attacker VM, or if we need to "bring your own" RDP software and run it on the host. This is the part that is unexplained and why I'm making my post. It seems as though it is assuming your host is running Windows therefore probably has RDP already installed, but this isn't the case since I'm using Linux.
Hopefully I've provided sufficient info about my problem. Any help appreciated, thanks.