How to update an issue with Rest API using C#

[THILAK thilz]

I am not getting any clue about updating an JIRA issue 

[Nic Brough -Adaptavist-]

Your code needs to perform REST calls, we can't help you with that, as you could be doing anything.

But the calls it needs to make to JIRA are pretty standard.  Start at https://developer.atlassian.com/jiradev/jira-apis/jira-rest-apis to get a feel for them.