how nuch does it cost to repair a screen of iphone 7plus in india

Try contacting some Authorised Service Providers and ask them : https://support.apple.com/en-in/iphone/repair/service

It really depends. Not sure where you are. You would need to have it done through a service provider there, and they have different prices as they are free to set them. However, not all service providers have access to Apple's equipment to test the device and make sure that the parts communicate with each other. If they don't have that equipment, it might cost more if they have to send it out.