Magento 2 – How to Add Attribute Flag to Quote Item

In order to save some additional details in quote items table, you need to first create a new column in sales_flat_quote_item table. Then only your save action will work.

Magento Sales Quotes and Sales Orders are not EAV entities. They are flat entities.

I am not sure about my below solution:

• May be you need to load Quote item object by item id
• As you want set price then using setPrice() you cannot set your desire price for that cart item

$item = $quote->getItemById($item->getId());
if (!$item) {
  continue;
}
$item->setQty((double) $qty);
$item->setCustomPrice($price);
$item->setOriginalCustomPrice($price);
$item->getProduct()->setIsSuperMode(true);
$item->save();