I am currently on unRAID 6.9 and I currently have one cache drive.

 

I would like to add a 1TB SSD and move Plex onto it.

 

Do I :

Create a cache pool with my existing cache drive and the 1TB SSD or do I add the 1TB SSD as an unassigned device?

How do I then move the Plex docker and all the files onto the SSD?

 

I would do neither of those

 

Since you are on UnRaid 6.9 you can have multiple pools so why not simply create another pool for Plex?

Ok so I create another pool, what is my next move? Does unRAID automatically move stuff over or do I have to manually move it.

You will have to move the data manually. (with the Docker system disabled)