Hi @sekhar_n,
I will suggest to use magento default import/export feature.
Update you csv required attributes and your additional field and import again with update behaviour.
For more info:
https://docs.magento.com/m2/ce/user_guide/system/data-import.html
If you familiar with Magento 2rest api then you can also update specific attributes using Magento 2 REST API as well.
I hope it will help you!
in csv file can i put these three attributes only(SKU MetaKeyword and Special Price) ?
Yes, you can put above three coulumn in the csv file.
I will suggest to downlaod the sample file and edit the same.
For more info,
magento-product-management/required-magento-2-import-values/