How to automatically reduce store items upon approval of internally requested items

Hi team,

We make use of internal requisition to request for stationery items in my Organization.

Upon approval of these requested items, the items in the store should reduce automatically but this is not the case.

E.g we have 408 quantity of A4 paper presently, once one A4 paper gets requested for and approved, it should reduce to 407 but we usually manually reduce the item quantity in store which should not be so.

Kindly assist.

see attachment