To track the inventory for the delivery challan, please follow below mentioned Steps.
Step 1: Please go to Settings.
Step 2: Click on Preferences under the General settings.
Step 3: Go to Products & Inventory section >> Go to Inventory section >> Enable tracking of inventory linked to delivery challans for better management >> Enable > Save Changes
Now whenever you are creating the Delivery challan, the stock will be automatically removed from the inventory.
Note : If track inventory for Delivery Challan is enabled, then the stock will be deducted while creating the Delivery Challan. If it is disabled, then the stock will remain same.