Magento 1.9 – How to update table values using CSV?

I want to add alt tags to my all 50K products so that i plan to update table catalog_product_entity_media_gallery_value. After created csv

https://i.stack.imgur.com/oHTU9.png

and directly imported to the table catalog_product_entity_media_gallery_value.

The value is not updated return error like INSERT INTO catalog_product_entity_media_gallery_valueVALUES (‘7653’, ‘0’, ‘951 Rose P’, ‘1’, ‘0’) Actualy i want to update, how to do that?

FYI: Value_id is Foreign key