Take value from one doctype into report

Hi… I have one doctype name as sales invoice item in which there is 1 field Quantity(kgs) as weight_per_unit. i want to take all the values of corresponding items into a report which is made in jason. please help.

{“columns”:[{“label”:“Item Code”,“fieldname”:“item_code”,“fieldtype”:“Link”,“options”:“Item”,“width”:120,“id”:“item_code”,“name”:“Item Code”,“editable”:false,“compareValue”:null},{“fieldname”:“crop”,“field”:“crop”,“fieldtype”:“Link”,“label”:“Crop”,“insert_after_index”:0,“link_field”:“item_code”,“doctype”:“Item”,“options”:“Crop Master”,“width”:100,“id”:“crop”,“name”:“Crop”,“editable”:false,“compareValue”:null},{“fieldname”:“variety”,“field”:“variety”,“fieldtype”:“Link”,“label”:“Variety”,“insert_after_index”:1,“link_field”:“item_code”,“doctype”:“Item”,“options”:“Variety Master”,“width”:100,“id”:“variety”,“name”:“Variety”,“editable”:false,“compareValue”:null},{“label”:“Item Name”,“fieldname”:“item_name”,“fieldtype”:“Data”,“width”:120,“id”:“item_name”,“name”:“Item Name”,“editable”:false,“compareValue”:null},{“label”:“Description”,“fieldname”:“description”,“fieldtype”:“Data”,“width”:150,“id”:“description”,“name”:“Description”,“editable”:false,“compareValue”:null},{“label”:“Sales Order”,“fieldname”:“sales_order”,“fieldtype”:“Link”,“options”:“Sales Order”,“width”:100,“id”:“sales_order”,“name”:“Sales Order”,“editable”:false,“compareValue”:null},{“label”:“Delivery Note”,“fieldname”:“delivery_note”,“fieldtype”:“Link”,“options”:“Delivery Note”,“width”:100,“id”:“delivery_note”,“name”:“Delivery Note”,“editable”:false,“compareValue”:null},{“label”:“Invoice”,“fieldname”:“invoice”,“fieldtype”:“Link”,“options”:“Sales Invoice”,“width”:120,“id”:“invoice”,“name”:“Invoice”,“editable”:false,“compareValue”:null},{“label”:“Posting Date”,“fieldname”:“posting_date”,“fieldtype”:“Date”,“width”:120,“id”:“posting_date”,“name”:“Posting Date”,“editable”:false},{“label”:“Customer Name”,“fieldname”:“customer_name”,“fieldtype”:“Data”,“width”:120,“id”:“customer_name”,“name”:“Customer Name”,“editable”:false,“compareValue”:null},{“label”:“Customer Group”,“fieldname”:“customer_group”,“fieldtype”:“Link”,“options”:“Customer Group”,“width”:120,“id”:“customer_group”,“name”:“Customer Group”,“editable”:false,“compareValue”:null},{“label”:“Item Group”,“fieldname”:“item_group”,“fieldtype”:“Link”,“options”:“Item Group”,“width”:120,“id”:“item_group”,“name”:“Item Group”,“editable”:false,“compareValue”:null},{“label”:“Company”,“fieldname”:“company”,“fieldtype”:“Link”,“options”:“Company”,“width”:80,“id”:“company”,“name”:“Company”,“editable”:false,“compareValue”:null},{“fieldname”:“parent_territory”,“field”:“parent_territory”,“fieldtype”:“Link”,“label”:“Parent Territory”,“insert_after_index”:10,“link_field”:“territory”,“doctype”:“Territory”,“options”:“Territory”,“width”:100,“id”:“parent_territory”,“name”:“Parent Territory”,“editable”:false,“compareValue”:null},{“label”:“Territory”,“fieldname”:“territory”,“fieldtype”:“Link”,“options”:“Territory”,“width”:80,“id”:“territory”,“name”:“Territory”,“editable”:false,“compareValue”:null},{“label”:“Cost Center”,“fieldname”:“cost_center”,“fieldtype”:“Link”,“options”:“Cost Center”,“width”:100,“id”:“cost_center”,“name”:“Cost Center”,“editable”:false,“compareValue”:null},{“label”:“Income Account”,“fieldname”:“income_account”,“fieldtype”:“Link”,“options”:“Account”,“width”:100,“id”:“income_account”,“name”:“Income Account”,“editable”:false,“compareValue”:null},{“label”:“Stock Qty”,“fieldname”:“stock_qty”,“fieldtype”:“Float”,“width”:100,“id”:“stock_qty”,“name”:“Stock Qty”,“editable”:false,“compareValue”:null},{“label”:“Stock UOM”,“fieldname”:“stock_uom”,“fieldtype”:“Link”,“options”:“UOM”,“width”:100,“id”:“stock_uom”,“name”:“Stock UOM”,“editable”:false,“compareValue”:null},{“label”:“Rate”,“fieldname”:“rate”,“fieldtype”:“Float”,“options”:“currency”,“width”:100,“id”:“rate”,“name”:“Rate”,“editable”:false,“compareValue”:null},{“label”:“Amount”,“fieldname”:“amount”,“fieldtype”:“Currency”,“options”:“currency”,“width”:100,“id”:“amount”,“name”:“Amount”,“editable”:false,“compareValue”:null},{“label”:“Total Tax”,“fieldname”:“total_tax”,“fieldtype”:“Currency”,“options”:“currency”,“width”:100,“id”:“total_tax”,“name”:“Total Tax”,“editable”:false,“compareValue”:null},{“label”:“Total Other Charges”,“fieldname”:“total_other_charges”,“fieldtype”:“Currency”,“options”:“currency”,“width”:100,“id”:“total_other_charges”,“name”:“Total Other Charges”,“editable”:false,“compareValue”:null},{“label”:“Total”,“fieldname”:“total”,“fieldtype”:“Currency”,“options”:“currency”,“width”:100,“id”:“total”,“name”:“Total”,“editable”:false,“compareValue”:null}]}

this is the custom report made by another person. i want to add a column in this as quantity in kgs

https://frappeframework.com/docs/v14/user/en/desk/reports/script-report