Hi Sheethal,
You can add the public IP ranges in Classless Inter-Domain Routing (CIDR) format. You can use a free online IP range to CIDR calculator to help (search engine will give many to choose from).
For example, say you wanted to allow IP range 104.87.85.176 - 104.87.85.179, you would enter 104.87.85.176/30 on the Networking blade of your Cosmos DB.
Please click Accept Answer and upvote if the above was useful. If something is unclear or you need additional assistance for a specific range, add a comment below.
Thanks.
-TP