It's hard to tell exactly how this works but judging from the tutorial's docker-compose.yml [0] it looks like this runs as a separate API next to Prometheus and you tell Prometheus to write [1] to Mimir. I'm unclear how reads work from it or maybe there is no read?
Maybe I'm completely misunderstanding.
[0] https://github.com/grafana/mimir/blob/main/docs/sources/tuto...
[1] https://github.com/grafana/mimir/blob/main/docs/sources/tuto...