What should I enter as server URL?
Just enter the Endpoint of your AWS Elastic-search Cluster.

Use port : "80".

the Complete url will be something like: 

XXX-XXX-XXX-XXXXXX.ap-southeast-1.es.amazonaws.com:80

First check are you able to access the Elastic-search , Try to telnet on the server:

telnet XXX-XXX-XXX-XXXXXX.ap-southeast-1.es.amazonaws.com 80

If it's not accessible make it available for your IP by changing the access policy .