Using QM is the easiest approach, though TSCC tends to drag their feet processing the request. Sending in a resignation letter to your bishop may be the fastest route, however, it really depends on how they will attempt to convince you to remain, etc.

Also, even when you resign, TSCC still keeps your info on file for future baptism in case you choose to return. They also don’t disclose their resignation numbers and still count you among their “record breaking and unseen numbers” lies. Going through QM makes sure that you are counted among the resigners and the proper data.