[Nandini]

You can follow steps as indicated in this article and set up formula type field with a value of Mod(Value({!Lead_Number__c}), #reps)+1
Link to the article: https://roundrobindistributor.com/what-is-round-robin/
Try out some Salesforce Apps for complex scenarios: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3000000DpgwTEAR

[Nandini]

Hey
For Case routing, you can use case assignment rules, but, the only limitation being, there can be only one active rule at a time. You can alternatively use omnichannel or can try routing through round-robin algorithm. Check out the blog for more details: https://roundrobindistributor.com/what-is-round-robin/
Try using Salesforce apps like: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3000000DpgwTEAR