How to correct quantities in shipped RTV?

If we ship RTV in RMS, and then we realise that the quantitiy on RTV is wrong - shippend quantitiy in the system is greater than actuall shipped quantity - how can we correct this?

Example:

RTV: shippedn quantitiy=100

Actual quantitiy=50

What concerns me is that after RTV shippment debit memo is created in ReIM for original qty (100).

Options that I'm considering:

• Create inventory adjustment in RMS for the discrepancy (50), and manually create credit memo for the supplier in ReIM
• Create PO for discrepancy and create receipt. Ideally, this would be self-billing PO that produces credit memo for supplier, but I'm not sure how to set this up