In the "Publisher" field put the name of your Publisher.
If you don't have a Publisher, you can be your own publisher. You can be your own publisher by registering to a PRO as a publisher (BMI, ASCAP, SESAC, etc.) or by signing up with an admin publishing company (Songtrust, Audiam, etc.).
Once you've registered, you'll put the name you gave your publishing company in the "Publisher" field.