How to add REGUH-KUNNR into DMEE Tree

Hello all experts,

I copied the standard DMEE Tree  SEPA_DD to a new DMEE Tree. In the new DMEE, I need updating the element "EndToEndId" using REGUH-KUNNR field. But I know that the DMEE uses FPAYH, FPAYHX structures to map the DMEE element nodes.  So I want to know how to add REGUH-KUNNR through  FPAYH, FPAYHX structures? Or could you tell me the link between payment table REGUH to FPAYH, FPAYHX structures?

And I want to know the mapping procedure to fetch data from payment tables such as REGHU to fill the DMEE elements through FPAYH, FPAYHX structures.

Thanks in advance.

Iris