func findThing(things []Thing, name string) *Thing {
      for i := range things {
        if things[i].Name == name {
          return &things[i]
        }
      }
      return nil
    }

Also you could just return i or -1, and the consuming code would be clear about what it was doing. Find the index. Update the item at the index.

    if location := findThing(things, name); location != -1 {
         things[location].Name = "updated"
    }