MongoDB BulkWrite update operation $set not working

How can i get the latest totalQuantity in below code after $inc: { totalQuantity: -el.loadingTotal } operation? I am stuck at this point. Any ideas??

promiseArray.push(
          Stock.updateOne(
            {
              index: el.index,
              product: el.product,
              batchNo: el.batchNo,
              agency,
              totalQuantity: { $gte: el.loadingTotal },
            },
            {
              $push: {
                reservations: {
                  loadingSheetId: sheetAfterSave._id,
                  reservedCaseQuantity: el.loadingCaseCount,
                  reservedUnitQuantity: el.loadingUnitCount,
                  reservedTotalQuantity: el.loadingTotal,
                },
              },
              $inc: { totalQuantity: -el.loadingTotal },
              $set: { currentQuantity:  },  // How can i get the updated totalQuantity here
            },
            {
              session: session,
            }
          )
        );