Create / insert data to vbap via additional tab B

Hello,

I added a zzfield in the additional Tab B and in the appended structure for VBAP:

But when a click to Save i don't find data in my table VBAP:

Some can help me to write the exact abap code to save data from additional tab B to the table VBAP. ?

And also in wish user-exit i have to do that?

Thank u very much.