I remember playing this game; if my memory serves me right, the name of the game had nothing to do with Game of Thrones, but inside the game there were characters from the series. In this mobile game you had a battle arena where you placed 5 characters, like Stannis Baratheon as a tank, Bronn and Tyrion as rogues, the Red Priestess as support/healer, and Lady Stoneheart as a witch/mage. The goal was to defeat the opposing team by using your characters’ abilities in the right sequence. There was also a story mode, but I don’t remember many details about that part.
I looked it up here and I think it would be Game Of Thrones Legends RPG. In it there are the 5 slots you mentioned and the way to defeat the opposing team.