Soon starting our GAS tour with RS group. We will arrive a day early and wondering about a place to eat dinner first night before joining group next day. thanks.
Trier is pretty small so I'd meander and see what looks good. There are 3-4 recommended options listed in the guidebook that you'll be receiving with the tour or might have already. One of my colleagues recently assisted on the GAS tour and said in her own free time enjoyed a meal at Kartoffelrestaurant Kiste in Trier.
It's been a good three or four years since I visited Trier but I also like Kartoffelkiste. Note that "Kartoffelkiste" means "potato crate" and that name is meaningful, so if you don't like potatoes go somewhere else.
Roman meals according original recipe in restaurant Zum Domstein at the central market in Trier, see www.domstein.de