Black Carbon Fiber Roof Molding Trim Kit for GMC 2019=$49.95 from Trulineautomotive.com
Or you could Google to see if junkyards may have it.
I recently just did the opposite on my GMC Terrain 2015, removing the covers and installing the roof rails. I purchased the rails from ebay for $100 and watched a you tube video on how to install. It was easy, easy and did not have to pay dealership $300+, I threw away the rail covers not thinking anyone would want them.
Anyway, watch the you tube videos on how to install and just do the reverse to un-install.
Peace & Good Luck!