Is there any method through which we can add multiple products at a time.

Here's the documentation on the product catalog API that allows you to manage individual product entries: https://community.lithium.com/t5/Ratings-and-Reviews/Integrate-your-product-catalog/ta-p/109449

Please reach out to your Lithium customer success manager as - depending on your setup - there might be ways to set up a regular sync for your product catalog and the one stored in community.