There are two ways to use DMR Gateway now that BrandMeister UK has finally accepted Talk Groups as the way to go, as I described over two years ago.
The first and definitive way is to follow my guide that I have already published in this series of articles.
The second way is only for those people who still cannot get their heads round individual talk groups in their radios and it concerns only a change to define the BrandMeister section with Dynamic Talk Group ReWrite commands, the link to the document describing this is here.
I am not going to describe it or how it works, as personally I feel that it is more complicated to do that than to get to grips with your code plugs.
There are articles to help you with that in these pages.