§1. Without prejudice to the prescript of can. 1681, the bishop is to entrust the instruction of these processes either in a stable manner or in individual cases to his tribunal, that of another diocese, or a suitable priest.
§2. If a judicial petition to declare the nullity of the same marriage has been introduced, however, the instruction is to be entrusted to the same tribunal.
Source: Code of Canon Law (Vatican.va)