Until that system has Talkgroups added to the DB page for that system, it will never show up in Sentinel. I think that's a limitation or rule that Uniden dictates.
You will need to manually create and enter the info and then scan the sites in 'Search' mode so you can find any active unknown talkgroups.
Hopefully someone here can walk you through manually setting up a Connect Plus system.
If you do find and confirm any talkgroups, submit them from the systems page I linked above and then it will show up in Sentinel in the future!