Step 1:

• Go to Products -> Search Products.

Step 2:

• Search for the product you want to adjust quantity.
• Click on "Edit" button of product you want to adjust quantity

Step 3:

• Click on item "Quantity".

Step 4:

Use Positive value in "Qty" to add quantity, for example '2' Use Negative value in "Qty" to deduct quantity, for example '-2'

Add quantity:

• Enter the quantity you want to add.
• Enter the Unit Cost of products. 
• Click on "Save" to adjust quantity.

Deduct quantity:

• Enter the quantity (Negative value for example '-2') you want to deduct.
• Enter the Unit Cost of products. 
• Click on "Save" to adjust quantity.