Custom Schema

Hi-

Please excuse my rather limited knowledge of HL7.

In Ensemble, I have a HL7 message that contains several Z segments.  I have created a custom schema to represent the new Z segments along with the new DocType Structure and Message Structure

How does Ensemble/Health Connect know which custom schema to use?  I believe it has to be indicated in the MSH segment somewhere, but not sure where exactly that would be.   Is the version simply updated with the new schema name or is there some other field?

TIA

Ken