§1. The following can give dimissorial letters for secular clergy: 1/ the proper bishop mentioned in can. 1016; 2/ an apostolic administrator and, with the consent of the college of consultors, a diocesan administrator; with the consent of the council mentioned in can. 495, §2, an apostolic pro-vicar and an apostolic pro-prefect.
§2. A diocesan administrator, apostolic pro-vicar, and apostolic pro-prefect are not to grant dimissorial letters to those who have been denied admission to orders by the diocesan bishop, the apostolic vicar, or the apostolic prefect.
Source: Code of Canon Law (Vatican.va)