First of all, if it is a head office or a branch office, it is a legal person-the head office.
If it is a parent company or a subsidiary, the subsidiary enjoys independent legal personality.
What you have to do now is the procedure of changing the branch into a subsidiary. Here, you have to go to the head office and ask to cancel the procedure of setting up a branch office and change it into its equivalent subsidiary. In addition, you belong to the internal organization adjustment of the company, and there may be some formalities that need to be verified and registered with the relevant administrative department! Specifically, I suggest you take a look at the relevant contents of People's Republic of China (PRC) Company Law.