This can be done in free roam at any point in the game. You need to use your wing suit for this. The church is located in the Tyrol area (east of the starting area, Aravis). The coordinates for the church are 4300S - 5278E. Head to Haupt Schwarzenspitze (3708S - 5309E). Use your wing suit to head down the mountain and crash into the church bell. If you mess up, retry the line over and over again.
Here is a video guide with English commentary!
Here is a playlist of guides for this game!
https://www.youtube.com/playlist?list=PL-HeW6XkKdUKDDGWFoBmJ...