how to assign ticket to role member when ticket created by email not just to default user on rounrobin manner

[Nic Brough -Adaptavist-]

Code. 

You'll need a post-function that can scan through the role and select the "next" user according to your round-robin rules.  See https://developer.atlassian.com/static/connect/docs/latest/modules/jira/workflow-post-function.html