“There is no process defined in the Constitution to split a state.”
The Constitution does not provide for seccession of the various states.
Article IV, section 3 gives rules for admitting NEW states, however (splitting states included):
New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
See post 34.