Odoo 14 (Sales - Purchase - Inventory )

my company work by the following Operations Routes :

Buy   and    Replenish on Order (MTO)

purchased upon the confirmation of a sales order

and the related PO will have the source document field (with the related SO Number ) in odoo as is , 

now 

I need to create new field  ( Many2one) in the PO  , Named " Related SO Contact " under the odoo as is field  ( source document )

so that when the sales teem create SO its related (auto created ) PO will have the 

source document :    SO 0007

Related SO Contact :  the customer name from the related SO

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A)   by odoo studio , i've created the new ( Many2one) field in the po 

B )   i've created new Automated action with the following data 

  Model  :  Purchase Order
​
Trigger : On Creation & Update

Action To Do : Create a new Record

Target Model : Sales Order

Trigger Fields : source document (purchase.order)

Match records with the following rule:

Source Document

contains "S0"

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what i need 

i need any help to 

A ) complete the automated action to work wright as it not completed wright now and not working  

OR 

B ) Execute python code in the automated action , so if any one could write it so i can copy and past