This has probably been covered somewhere but I can’t find it.
Here’s my problem.
That was a very exhaustive video, I’m not going to lie, I didn’t watch the whole thing. But it sounds like you might be trying to add a linked data types field.
If that’s the case, that’s not how linking works. You link the data type, and can later on access the fields attached to it. So if you have a patient data type, you don’t do name = patients last name.
You do “patient = current/parent groups patient” or what have you.
If you then want to display the first name of a patient you would do something like “this case’s patient’s patient first name”
Does any of that makes sense? or maybe this is not what you’re facing at all. I just scrubbed through the video 
Thanks for your response I will try your solution and let you know. But I think you are right, I’m a noob at this and this linking data thing has me confused.